| #Q001 | treatment | treatment | recommended | Surface Water Treatment Filtration and Disinfection | drinking water | Treatment of surface water sources or GUDI should include adequate filtration (or technologies providing an equivalent log reduction credit) and disinfection. | When treating surface water sources or groundwater under the direct influence of surface waters (GUDI) | high |
| #Q002 | treatment | treatment | recommended | Groundwater Viral Reduction Target | drinking water | Treatment of groundwater sources should include a minimum 4 log (99.99%) removal and/or inactivation of enteric viruses. | When treating groundwater sources | high |
| #Q003 | operational | operational | recommended | Maintenance of Disinfectant Residual | drinking water | In systems with a distribution system, a disinfectant residual should be maintained throughout the system at all times. | In systems with a distribution system | high |
| #Q004 | monitoring | operational | recommended | E. coli Treatment Plant Monitoring Frequency | drinking water | E. coli should be monitored at least weekly in water leaving a treatment plant. | For municipal-scale drinking water supply systems | high |
| #Q005 | monitoring | operational | recommended | Use of Operational Indicators with E. coli Tests | drinking water | E. coli tests should be used in conjunction with other operational indicators, such as residual disinfectant and turbidity monitoring as part of a source-to-tap or water safety plan approach. | During monitoring in water leaving the treatment plant | high |
| #Q006 | monitoring | operational | recommended | Distribution and Storage Systems E. coli Monitoring Frequency | drinking water | In municipal-scale distribution and storage systems, the number of samples collected for E. coli testing should reflect the size of the population being served, with a minimum of four samples per month. | In municipal-scale distribution and storage systems | high |
| #Q007 | monitoring | operational | recommended | Use of Operational Indicators in Distribution System | drinking water | Operational indicators (e.g., disinfectant residual, pressure monitoring) should be used in conjunction with E. coli tests as part of a source-to-tap or water safety plan approach. | Within water distribution and storage systems | high |
| #Q008 | reporting | health | recommended | Notification of E. coli Detection | drinking water | If E. coli is detected in a sample of drinking water from a municipal-scale drinking water system (i.e. water leaving a treatment plant, or in a distribution or storage system), the system owner/operator and the laboratory processing the samples should immediately notify the responsible authorities. | If E. coli is detected in a sample | high |
| #Q009 | corrective_action | operational | recommended | Immediate Corrective Actions Following Detection | drinking water | The system owner/operator should also: immediately resample and test the E. coli -positive site(s) and adjacent sites; conduct an assessment to ensure treatment barriers are operating correctly (this may include gathering information on water treatment performance and other operational monitoring data); and carry out any corrective actions necessary (See Section 3.1.4) in order to resume control or normal system operations. | Upon detection of E. coli | high |
| #Q010 | corrective_action | health | recommended | Issuance of Boil Water Advisory | drinking water | If resampling and testing confirm the presence of E. coli in drinking water, the system owner/operator should immediately issue a boil water advisory in consultation with the responsible authorities, and carry out the appropriate corrective actions | If resampling and testing confirm the presence of E. coli | high |
| #Q011 | administrative | health | recommended | Cooperation in Surveillance | drinking water | The owner/operator should also cooperate with the responsible authorities in any surveillance for possible waterborne disease outbreaks. | Following detection and confirmation of E. coli | high |
| #Q012 | corrective_action | health | recommended | Immediate Advisory Trigger Conditions | drinking water | A boil water advisory should be immediately issued where there is evidence of: a significant failure of a critical treatment barrier; or illness in the community that is suspected to be associated with drinking water. | Where there is evidence of treatment barrier failure or suspected waterborne illness | high |
| #Q013 | corrective_action | operational | recommended | List of Appropriate Corrective Actions | drinking water | If resampling and testing confirms the presence of E. coli in drinking water, the owner/operator of the waterworks system should carry out appropriate corrective actions, which could include the following measures: Verify the integrity and the optimal operation of the treatment process. Verify the integrity of the distribution system. Verify that the required disinfectant residual is present throughout the distribution system. Increase disinfectant dosage, flush water mains, clean treated-water storage tanks (municipal reservoirs and domestic cisterns), and check for the presence of cross-connections and pressure losses. | If resampling confirms presence of E. coli | high |
| #Q014 | monitoring | operational | recommended | Minimum Resampling Locations | drinking water | At a minimum, one sample upstream and one downstream from the original sample site(s) plus the treated water from the treatment plant as it enters the distribution system should be tested. | During corrective action resampling | high |
| #Q015 | administrative | health | guidance | Conditions for Rescinding Boil Water Advisory | drinking water | Once the appropriate corrective actions have been taken and only after a minimum of two consecutive sets of bacteriological samples, collected 24 hours apart, produce negative results, an E. coli -related boil water advisory may be rescinded. | To rescind an E. coli-related boil water advisory | high |
| #Q016 | monitoring | health | recommended | Private Well Routine Testing | drinking water | Homeowners with private wells should regularly test (at a minimum two times per year) their well for E. coli , ideally during these same at-risk times. | For private wells in residential-scale drinking water systems | high |
| #Q017 | monitoring | health | recommended | Testing of New or Rehabilitated Wells | drinking water | New or rehabilitated wells should also be tested before their first use to confirm microbiological safety. | Before first use of new or rehabilitated wells | high |
| #Q018 | administrative | operational | recommended | Compliance with Authority Requirements for Residential Systems | drinking water | Residential-scale systems that serve the public may be subject to regulatory or legislative requirements and should follow any actions specified by the responsible drinking water authority. | For residential-scale systems serving the public | high |
| #Q019 | reporting | health | recommended | Notification of E. coli Detection in Residential Systems | drinking water | If E. coli is detected in a sample of drinking water from a residential-scale system that serves the public, the system owner/operator and the laboratory processing the samples should immediately notify the responsible authorities. | If E. coli is detected in a residential-scale system serving the public | high |
| #Q020 | monitoring | operational | recommended | Immediate Resampling in Residential Systems | drinking water | The system owner/operator should also immediately resample and test the drinking water to confirm the presence of E. coli. | Following an initial positive E. coli test in a residential-scale system serving the public | high |
| #Q021 | corrective_action | health | recommended | Private Supply Advisory Action | drinking water | If E. coli is detected in a private drinking water supply, homeowners should also be advised to boil their drinking water or to use an alternative supply that is known to be safe; and to resample and test their drinking water to confirm the presence of E. coli. | If E. coli is detected in a private drinking water supply | high |
| #Q022 | corrective_action | operational | recommended | Corrective Actions Upon Confirmation in Residential Systems | drinking water | If resampling confirms that the source is contaminated with E. coli , the system owner/operator should immediately carry out the appropriate corrective actions (see Section 3.2.3 and 3.2.4). | If resampling confirms E. coli contamination | high |
| #Q023 | corrective_action | operational | recommended | Fault Correction in Disinfected Supplies | drinking water | The first step, if it has not already been taken, is to evaluate the physical condition of the drinking water system as applicable... Any identified faults should be corrected. | As part of corrective actions for disinfected supplies | high |
| #Q024 | monitoring | operational | recommended | Verification Resampling After Corrective Actions | drinking water | After the necessary corrective actions have been taken, samples should be collected and tested for E. coli to confirm that the problem has been corrected. | Following corrective actions in residential supplies | high |
| #Q025 | corrective_action | operational | recommended | Fault Evaluation in Undisinfected Wells | drinking water | The first step, if it has not already been taken, is to evaluate the condition of the well, well head, pump, plumbing, and surrounding area. Any identified faults should be corrected. | As part of corrective actions for undisinfected wells | high |
| #Q026 | corrective_action | operational | recommended | Shock Chlorination and Flushing for Undisinfected Wells | drinking water | If the physical conditions are acceptable, then the following corrective actions should be carried out: Shock-chlorinate the well and plumbing system. Flush the system thoroughly and retest to confirm the absence of E. coli. | If physical conditions are acceptable in an undisinfected well following contamination | high |
| #Q027 | monitoring | operational | recommended | Delay of Confirmatory Tests | drinking water | Confirmatory tests should be delayed until either 48 hours after tests indicate the absence of a chlorine residual or five days have elapsed since the well was treated. | Following shock-chlorination of a well | high |
| #Q028 | administrative | health | recommended | Conditions for Rescinding Boil Water Advisory for Residential Systems | drinking water | Once the appropriate corrective actions have been taken, an E. coli -related boil water advisory should be rescinded only after a minimum of two consecutive sets of samples, collected 24 hours apart, produce negative results. | To rescind an E. coli-related boil water advisory for residential-scale systems | high |
| #Q029 | monitoring | operational | recommended | Follow-Up Testing Post-Contamination | drinking water | Additional tests should be taken after three to four months to ensure that the contamination has not recurred. | Following the rescinding of a boil water advisory in residential systems | high |
| #Q030 | administrative | operational | recommended | Analysis Approval Requirements | drinking water | All analyses for E. coli should be carried out as directed by the responsible drinking water authority. | | high |
| #Q031 | administrative | operational | recommended | Quality Assurance Program | drinking water | To ensure reliable results, a quality assurance program, which incorporates quality control practices, should be in place. | During laboratory or in-house analysis | high |
| #Q032 | operational | operational | recommended | Test Kit Manufacturer Instructions | drinking water | Analyses conducted using test kits used should be performed according to the manufacturer's instructions. | When analyses are conducted using test kits | high |
| #Q033 | monitoring | operational | mandatory | Representative Sample Collection Procedures | drinking water | Proper procedures for collecting samples must be observed to ensure that the samples are representative of the water being examined. | During sample collection | high |
| #Q034 | monitoring | operational | guidance | Sample Location Selection | drinking water | Sample collectors are also advised to carefully choose sample locations, avoiding (or alternatively disinfecting) taps subject to external contamination (e.g., close to a sink bottom or the ground) and taps of questionable cleanliness | During sample collection | high |
| #Q035 | monitoring | operational | recommended | Sample Packing Instructions | drinking water | Generally, samples for microbiological testing should be packed with ice packs but protected from direct contact with them to prevent freezing. | During sample packing | high |
| #Q036 | monitoring | operational | recommended | Sample Transport Temperature | drinking water | During transport, samples should be kept cool but unfrozen at temperatures between 4 and 10°C | During transport of samples | high |
| #Q037 | monitoring | operational | recommended | Prompt Sample Analysis | drinking water | To avoid unpredictable changes in the bacterial numbers of the sample, E. coli samples should always be analyzed as soon as possible after collection. | Following sample collection | high |
| #Q038 | monitoring | operational | recommended | Maximum Holding Time Recommendation | drinking water | Ideally, for E. coli analysis of drinking water samples, the holding time between the collection of the sample and the beginning of its examination should not exceed 30 hours | Before examination of samples | high |
| #Q039 | monitoring | operational | recommended | Action Upon Sample Rejection | drinking water | When a sample is rejected, it is recommended that utilities immediately collect and submit a resample from that test location. | If a sample is rejected due to holding time requirements | high |
| #Q040 | monitoring | operational | recommended | Sample Labelling | drinking water | Samples should be labelled according to the requirements specified by the responsible drinking water authority and the analytical laboratory. | During sample handling | high |
| #Q041 | monitoring | operational | recommended | Sample Volume for Analysis | drinking water | To obtain a reliable estimate of the number of E. coli in treated drinking water, a minimum volume of 100 mL of water should be analyzed. | During E. coli analysis | high |
| #Q042 | monitoring | operational | recommended | Operational and Verification Monitoring Parameters | drinking water | As part of operational and verification monitoring in a drinking water quality management system using a source-to-tap or water safety plan approach, water leaving a treatment plant and within the distribution system should be tested at least weekly for E. coli and daily for disinfectant residual and turbidity. | During routine operational and verification monitoring | high |
| #Q043 | monitoring | operational | recommended | Increased Sampling Based on Population | drinking water | The number of samples for bacteriological testing should be increased in accordance with the size of the population served. | When determining bacteriological testing frequency | high |
| #Q044 | monitoring | operational | recommended | Testing of New or Rehabilitated Wells Before First Use | drinking water | New or rehabilitated wells should also be sampled before their first use to confirm acceptable bacteriological quality. | Before first use of a well | high |
| #Q045 | monitoring | operational | recommended | Concurrent Disinfectant Residual Testing | drinking water | Disinfectant residual tests should be conducted when bacteriological samples are taken. | When bacteriological samples are taken | high |
| #Q046 | administrative | operational | mandatory | Approval of Sampling Locations | drinking water | In municipal-scale systems, the location of sampling points must be selected or approved by the responsible drinking water authority. | In municipal-scale systems | high |
| #Q047 | monitoring | operational | recommended | Representative Sample Sites Selection | drinking water | Sample sites should include the point of entry into the distribution system and points in the distribution systems that are representative of the quality of water supplied to the consumer. | When selecting sample sites | high |
| #Q048 | operational | operational | recommended | Evaluation of Subsurface Sources | drinking water | Subsurface sources should be evaluated to determine whether the supply is susceptible to contamination by enteric viruses and protozoa. | For subsurface source supplies | high |
| #Q049 | operational | treatment | recommended | Distribution System Disinfectant Residual | drinking water | In systems with a distribution system, a disinfectant residual should be maintained at all times. | In systems with a distribution system | high |
| #Q050 | operational | operational | mandatory | Process Control and Operator Training | drinking water | Adequate process control measures and operator training are also required to ensure the effective operation of treatment barriers at all times | To ensure effective operation of treatment barriers | high |
| #Q051 | monitoring | operational | recommended | Distribution System Operations and Maintenance | drinking water | Water quality in the distribution system should be regularly monitored (e.g., microbial indicators, disinfectant residual, turbidity, pH), operations/maintenance programs should be in place (e.g., water main cleaning, cross-connection control, asset management) and strict hygiene should be practiced during all water main construction, repair or maintenance to ensure drinking water is transported to the consumer with minimum loss of quality | For distribution systems | high |
| #Q052 | operational | treatment | recommended | Optimization for Chloramine Stability | drinking water | When chloramine is used as a residual disinfectant in drinking water distribution systems, treatment processes should be optimized for chloramine stability (Cl2:NH3 weight ratio of 4.5:1 – 5:1, pH > 8.0) | When chloramine is used as a residual disinfectant | high |
| #Q053 | operational | operational | recommended | Private Well Susceptibility Assessment | drinking water | In cases where an individual household obtains its drinking water from a private well, the susceptibility of the source to fecal contamination should be assessed. | For individual households with private wells | high |
| #Q054 | treatment | health | recommended | Point-of-Use Device Deployment | drinking water | Because of the potential public health risks from the use of microbiologically-contaminated drinking water, if POU devices are used instead of a point-of-entry system, all points of water used for drinking, food and beverage preparation, hygiene or washing dishes should be equipped with point-of-use treatment devices. | If POU devices are used instead of a POE system | high |
| #Q055 | treatment | operational | recommended | Certification of Hypochlorite Solutions | drinking water | Residential-scale supplies that use liquid chlorine should use hypochlorite solutions that are certified as meeting NSF/ANSI/CAN Standard 60... and follow the handling and storage recommendations for hypochlorite... | For residential-scale supplies using liquid chlorine | high |
| #Q056 | treatment | operational | recommended | UV System Installation Constraint | drinking water | They [UV systems certified to NSF/ANSI Standard 55 Class A] are not designed to treat wastewater or water contaminated with raw sewage and should be installed in visually clear water. | When installing UV systems certified to NSF/ANSI Standard 55 Class A | high |
| #Q057 | monitoring | operational | recommended | Testing Effectiveness of Treatment Devices | drinking water | To verify that the treatment device is effective, the system owner/operator or homeowner should periodically test both the water entering the treatment device and the treated water for E. coli and total coliforms using an accredited laboratory. | To verify treatment device effectiveness | high |
| #Q058 | operational | operational | recommended | Maintenance Schedule for Treatment Devices | drinking water | Consumers should verify the expected longevity of the components in their treatment device according to the manufacturer's recommendations and establish a clearly defined maintenance schedule. | For consumers using treatment devices | high |
| #Q059 | operational | operational | recommended | Inspection and Servicing of Treatment Devices | drinking water | Treatment devices should be inspected and serviced in accordance with the maintenance schedule and manufacturer's recommendations. | For consumers using treatment devices | high |
| #Q060 | corrective_action | operational | recommended | Dechlorination Consultation | drinking water | The responsible authority should be consulted regarding the correct procedure for dechlorinating water being discharged into the environment. | During corrective actions involving flushing water mains or cleaning tanks | high |
| #Q061 | administrative | operational | recommended | Well Construction Consultation | drinking water | The responsible drinking water authority in the affected jurisdiction should be consulted regarding their specific requirements for well construction and maintenance. | For residential-scale systems and private wells | high |
| #Q062 | monitoring | operational | recommended | Storage Data Recording | drinking water | When analysis will be delayed, it is particularly important to record the duration and temperature of storage, as this information should be taken into consideration when interpreting the results. | When sample analysis is delayed | high |
| #Q063 | design | treatment | recommended | Residential Surface Water Restriction | drinking water | In general, surface water is not recommended as a residential-scale water supply unless it is properly filtered, disinfected and monitored for water quality. | For residential-scale water supplies | high |
| #Q064 | monitoring | operational | recommended | Event-based Sampling Consideration | drinking water | Water utilities should consider additional sampling during these events [spring runoff, storms or wastewater spills]. | During events that lead to changes in source water conditions | high |
| #Q065 | administrative | operational | recommended | Laboratory Holding Time Protocol Discussion | drinking water | Water utilities should also discuss with the laboratory, the protocols for rejecting or analysing samples that exceed holding time specifications. | Regarding sample holding time specifications | high |
| #Q066 | administrative | operational | recommended | Onsite Testing Consultation | drinking water | Water utilities should first consult with the responsible drinking water authority about the acceptability of this practice [onsite testing with commercialized test methods] and any other requirements that may apply. | When long holding times are anticipated and onsite testing is considered | high |
| #Q067 | monitoring | operational | recommended | Multi-source Sampling Coverage | drinking water | If the water supply is obtained from more than one source, the location of sampling sites should ensure that water from each source is periodically sampled. | If the water supply is obtained from more than one source | high |
| #Q068 | operational | treatment | mandatory | Treatment Target Achievement Location | drinking water | It is essential that the removal and inactivation targets are achieved before drinking water reaches the first consumer in the distribution system. | For municipal-scale treatment systems | high |
| #Q069 | administrative | operational | recommended | Consultation on Analytical Method Selection | drinking water | When purchasing laboratory services or selecting analytical methods for analysis to be performed in-house, water utilities should consult with the analytical laboratory or manufacturer on issues of method sensitivity, specificity and turnaround time. | When purchasing laboratory services or selecting analytical methods | high |
| #Q070 | operational | operational | recommended | Loose Ice Prohibition | drinking water | Packing the sample with loose ice is not recommended as it may contaminate the sample. | During sample packing and transport | high |
| #Q071 | administrative | operational | recommended | Trucked Water Guidance Consultation | drinking water | Specific guidance related to the operation, maintenance and monitoring requirements for trucked water systems and drinking water cisterns or storage tanks should be obtained from the responsible drinking water authority in the affected jurisdiction. | For trucked water systems and drinking water cisterns or storage tanks | high |
| #Q072 | reporting | health | guidance | Discretionary Immediate Notification Trigger | drinking water | where E. coli contamination is detected in the first sampling—for example, E. coli -positive sample results from a single site, or from more than one location in the distribution system—the owner/operator or the responsible authority may decide to notify consumers immediately to boil their drinking water or use an alternative supply known to be safe and initiate corrective actions without waiting for confirmation. | Where E. coli contamination is detected in the first sampling | high |
| #Q073 | corrective_action | operational | guidance | Shock Chlorination for UV Systems | drinking water | For systems where the disinfection technology does not leave a disinfectant residual, such as ultraviolet (UV), it may be necessary to shock chlorinate the well and plumbing system. | For systems where disinfection technology does not leave a residual | high |
| #Q074 | monitoring | operational | guidance | Authority-led Post-Advisory Monitoring | drinking water | Additional water quality monitoring and actions may be required by the responsible drinking water authority. | When rescinding a boil water advisory | high |
| #Q075 | monitoring | operational | guidance | Glucuronidase Enzyme Verification Method | drinking water | E. coli confirmation can also be done by subjecting coliform-positive samples to media that tests for the β-D-glucuronidase enzyme | When verification of a positive test result is required | high |
| #Q076 | monitoring | operational | mandatory | Treatment Plant Testing Frequency Specification | drinking water | The required frequency for all testing at the treatment plant is specified by the responsible drinking water authority. | For municipal-scale drinking water supply systems | high |
| #Q077 | administrative | operational | guidance | Authority-Determined Post-Shock Practice | drinking water | For residential-scale systems that serve the public, the responsible drinking water authority may determine acceptable practice [regarding retesting after shock chlorination]. | For residential-scale systems serving the public following shock chlorination | high |
| #Q078 | administrative | operational | recommended | Consultation with Authority for Specific Requirements | drinking water | Water system owners should contact the appropriate drinking water authority in the affected jurisdiction to confirm the specific requirements that apply to their system. | When verifying the quality of treated drinking water | high |
| #Q079 | monitoring | operational | mandatory | Distribution System Monitoring Specification | drinking water | The frequency and sampling points for E. coli testing within distribution and storage systems will be specified and/or approved by the responsible drinking water authority. | In municipal-scale distribution and storage systems | high |
| #Q080 | monitoring | operational | mandatory | Residential System Frequency Determination | drinking water | Testing frequencies for residential-scale systems are determined by the responsible drinking water authority in the affected jurisdiction | For residential-scale systems | high |
| #Q081 | corrective_action | operational | recommended | Well Reconstruction or Replacement Consideration | drinking water | If these factors cannot be identified or corrected, either an appropriate disinfection device or well reconstruction or replacement should be considered. | If water remains contaminated after shock-chlorination in undisinfected wells | high |
| #Q082 | monitoring | operational | recommended | Residential Testing Frequency Timing | drinking water | Testing frequencies for residential-scale systems are determined by the responsible drinking water authority in the affected jurisdiction, and should include times when the risk of contamination of the drinking water source is the greatest, for example, in early spring after the thaw, after an extended dry spell, or following heavy rains. | When determining testing frequencies for residential-scale systems | high |
| #Q083 | administrative | health | recommended | Responsible Authority Advisory Duty | drinking water | The responsible authority should advise the system owner/operator to boil the drinking water or to use an alternative supply that is known to be safe in the interim. | If E. coli is detected in a sample from a residential-scale system serving the public | high |
| #Q084 | operational | treatment | recommended | Residential Disinfection System Maintenance | drinking water | Ensure that the disinfection system is working properly and maintained according to manufacturer's instructions. | As part of corrective actions for disinfected residential supplies | high |
| #Q085 | monitoring | operational | recommended | Corrective Action Monitoring Parameters | drinking water | Tests performed should include those for E. coli, total coliforms (as a general indicator of microbiological quality and inadequate treatment) and operational monitoring parameters such as disinfectant residual and turbidity. | During investigative and corrective action sampling in municipal systems | high |
| #Q086 | corrective_action | operational | recommended | Investigation of Problem and Prevention of Recurrence | drinking water | Conduct an investigation to identify the problem and prevent its recurrence; this would include measuring raw water quality (e.g., bacteriology, turbidity, colour, natural organic matter, and conductivity) and variability. | If resampling and testing confirms the presence of E. coli in drinking water | high |
| #Q087 | monitoring | operational | recommended | Follow-up Sampling during Investigative Phase | drinking water | Continue selected sampling and testing (e.g., bacteriology, disinfectant residual, turbidity) of all identified sites during the investigative phase to confirm the extent of the problem and to verify the success of the corrective actions. | During the investigation of E. coli contamination in municipal-scale systems | high |
| #Q088 | corrective_action | operational | recommended | Flushing Technique Identification and Implementation | drinking water | It is therefore important that water utilities identify and implement the most appropriate flushing technique for addressing the particular microbiological water quality issue of concern. | When implementing flushing as a corrective action in response to fecal contamination | high |
| #Q089 | monitoring | operational | recommended | Sampling Following Extreme Weather Events | drinking water | Water utilities impacted by such events [extreme weather events] should consider conducting additional sampling during and/or following their occurrence. | Following extreme weather events such as intense rainfall, flash floods, hurricanes, droughts and wildfires | high |
| #Q090 | corrective_action | operational | recommended | Dechlorination Consultation for Residential Disinfected Systems | drinking water | The responsible authority should be consulted regarding the correct procedure for dechlorinating water that may be discharged into the environment. | During corrective actions for residential-scale disinfected supplies | high |
| #Q091 | corrective_action | operational | recommended | Dechlorination Consultation for Undisinfected Well Flushing | drinking water | The responsible authority should also be consulted regarding the correct procedure for dechlorinating water that may be discharged to the environment. | During flushing and retesting of undisinfected residential wells | high |
| #Q092 | corrective_action | operational | recommended | Disinfectant Dosage and Storage Tank Cleaning for Residential Systems | drinking water | Increase the disinfectant dosage; flush the system thoroughly and clean treated water storage tanks and domestic cisterns. | If physical conditions are acceptable in a contaminated disinfected residential system | high |
| #Q093 | corrective_action | operational | recommended | Investigation of Persistent Residential Well Contamination | drinking water | If the water remains contaminated after shock-chlorination, further investigation into the factors likely contributing to the contamination should be carried out. | If contamination persists in residential wells after initial corrective actions | high |