(References in parentheses are to the Risk Information Table.) Risk Information Table Reliable information about water quality is essential for the proper management of a water supply. Knowledgeable and skilled staff are also essential for minimising the public health risks associated with water supplies. Please read the staff training (Guide G1) and the monitoring guides (Guide G2). While we haven’t pointed out every detail of how these documents are linked with the present document, the links are many and are important. Abbreviations: DWSNZ – Drinking-Water Standards for New Zealand Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: INTRODUCTION OF CONTAMINATION BY PRESSURE FLUCTUATIONS Possible hazards: Germs and chemical determinands (depending on the nature of the contamination source). Level of risk: High1 D2.2.1.1 Mains pressure failure elsewhere, or high demand. Model network analysis to identify potential problem pressure areas. Regular on hydrant flows or correlation of fire service data with water supplier’s pressure and flow data. Planned replacement and/or relining of mains. Develop programmes to carry out annual leak detection and undertake repairs. Record: customer complaints fire service feedback. Implement water conservation policy – eg, restrictions on garden watering, public appeals to reduce demand. Increase flow rate of treatment plant. Drop the pressure in the whole system or part of it. Flows. Pressures. Demand. Treatment plant output. quality. Increase in flow above normal rates. Pressure fluctuations. Reservoir levels outside normal diurnal pattern. E. coli or coliforms detected in 100 ml water sample. Revisit network to identify potential problem areas better. Review pumping regime out of zone. Review replacement programme. Ensure backflow valves are installed at properties and audited to assess correct operation (see Guide D2.4). Modify water conservation strategy. 1 Low pressure can back-siphonage. Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed INTRODUCTION OF CONTAMINATION BY PRESSURE FLUCTUATIONS cont’d
D2.2.1.2 Pipe failure or accidental penetration. Continuously monitor flow measurements from treatment plants and reservoirs. Set maximum response times to customer complaints and failures, and have procedures in place to isolate failures to minimise their impacts. Establish and publicise phone line. Identify critical areas of poor quality pipe. Flows. Pressures. Frequency and location of pipe failures. quality. Pipe failure rate higher than average expected from pipe condition. number of breaks because underground protocol not followed. E. coli detected in 100 ml water sample. Review network model to optimise pressure and flow. Define a protocol for contractors doing underground work on other services, and check that it is being adhered to. Develop and adhere to programmed annual work as per Asset Plan. Develop pressure control programme for whole system, or selected zones, including use of: ancillary sources – eg, pressure valves and pressure sustaining valves reservoir levels, etc. Undertake an annual leak detection programme on the whole system or selected zones. Ensure suitable materials are used for network construction (see Guide D2.1). Revise contractor protocol. Event: INTRODUCTION OF CONTAMINATION BY PRESSURE FLUCTUATIONS cont’d D2.2.1.3 Unpredicted event such as a major fire. Regularly check that air valves are working effectively. Undertake immediate investigation of water complaints. Locate reservoirs at elevations that minimise pressure Make sure recommended fire-fighting reserves of water are maintained. Use a pressure booster, if ancillary sources are available. Reservoir levels. Pressure. Consumer complaints. quality. Pressure outside normal range. Consumers complain about dirty water and lack of pressure. E. coli or coliforms detected in 100 ml water sample after the event. Re-examine network model to determine ways of sustaining pressure under these
D2.2.1.4 Failure of network pumps pumping to high zones or reservoirs (see Guide P10). Standby pump with auto start. Obtain generator backup. Preventive maintenance programme for pumps. Pumps. Pressure. quality. Pump stops. Customer complaints. Pressure drops. E. coli or coliforms detected in 100 ml sample. Re-route water from other zones if possible. Start preventive maintenance programme. D2.2.1.5 Failure of bore pumps (for systems with bores). Monitor bore performance either directly or using an observation bore. Preventive maintenance programme for bore pumps and planed programme for overhaul of pumps (see Guide P10). Monitor flow from bore. Monitor reticulation system pressure. Bore flow. Pressure. quality. Bore pumps stop. Reduced flow from bores. Reduced pressure in bore-fed reticulation zone. E. coli or coliforms detected in 100 ml water sample. Identify reasons for bore pump failure, and rectify. preventive maintenance programme. 2 This event may lead to discolouration of water and the release of bacteria that were previously protected by the sediment and deposits in the pipes. Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: RE-SUSPENSION OF SEDIMENT OR BIOFILM WITHIN THE MAINS BY PRESSURE FLUCTUATIONS Possible hazards: Germs; chemical determinands. Level of risk: Low–moderate D2.2.2.1 Sediment or biofilm allowed to develop. See Guide D2.3 – Event D2.3.2. Although D2.3.2 deals with re-suspension of material after repair of a mains break or attachment of a fitting, the net effect and the risks are the same as re-suspension of material already in the mains. D2.2.2.2 Significant fluctuations in reticulation pressure. See D2.3 – Event D2.3.2. Although D2.3.2 deals with re-suspension of material after repair of a mains break or attachment of a fitting, the net effect and the risks are the same as re-suspension of material already in the mains. Contingency Plans