Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: NOT ENOUGH WATER Possible hazards: Hazards associated with poor hygiene. Level of risk: High C1.4.1 Too little rainfall as well as too little storage, high use of water, or a leak in tank or guttering. Make sure tank is big enough. Make sure guttering is strong enough for wind and snowfall conditions. Check tank and guttering monthly for leaks. Stop unnecessary use of water. Water level in tank. Rate of water use. Water supply often runs out. Water level is low. Signs of water leaking from tank. Get new tank. Find a new or additional source of water. Repair tank and/or guttering. Take steps to save water. C1.4.2 Mechanical failure of pump (header tank short of water). Do preventive maintenance on pump: daily visual inspections lubrication seal replacement leaks repaired corroded components replaced annual ammeter tests. Planned maintenance programme for replacement of pump parts (follow per manufacturer’s recommendations). Pump maintenance log. Frequent pump breakdowns. Pump maintenance not being done. Revise, or put in place a pump maintenance schedule. C1.4.3 Power failure to pump. Install an alarm that warns that the power has failed. Install a stand-by generator. Regularly maintain the power supply (if you have a diesel generator, for example). Alarm. Electricity supply. Water flow. Alarm is triggered. No electricity reaching the pump. No water flow to header tank when pump should be operating. Make arrangements to get a more reliable power supply.
Cartridge filtration Event: FILTER NOT REMOVING PARTICLES DOWN TO 2 µm IN SIZE Possible hazards: Large germs (Giardia and Cryptosporidium not removed). Level of risk: High4 C1.5.1 Wrong type of cartridge filter. Use filters that are certified to remove particles down to 2 m in size. Make sure filter cartridge is compatible with the filter housing and note the type of filter used. National or international certificate of filter’s capabilities.5 Record of filter types used. Cloudiness in the water following filtration. Customer complaints. Cases of diarrhoea in people drinking the water. Wrong filter type used. Change to a different type of filter. Keep list of filters that match the housing in use. C1.5.2 Damage to the seal between the cartridge and filter housing. Check the condition of the filter housing and the cartridge seal when changing filters. Make sure the person replacing the cartridges knows the correct way to do it. The state of the filter seal. Filter maintenance log. Appearance of the water. Cloudiness in the water following filtration. Customer complaints. Cases of diarrhoea in people drinking the water. Frequent damage to seal. Decide whether the cartridge or housing is damaged, and replace damaged unit. Train staff in replacing cartridges if necessary. Read filter manufacturer’s instructions. C1.5.3 Cartridge not properly seated in the mounting. Make sure the cartridge is fitted the correct way round (some only work one way). Make sure base of filter housing is wiped clean before reseating filter cartridge. Make sure cover is replaced properly. Check, directly after re-seating it, that the filter is removing particles. (Checks are described in Sections 3.2.3.1 and 11 of DWSNZ: 2000). Make sure the person replacing the cartridges knows the correct way to do it. Results from particle removal checks. Appearance of the water. Cloudiness in the water following filtration. Filter unable to remove more than 99.9% of particles greater than 2 µm in size entering it. Customer complaints. Cases of diarrhoea in people drinking the water. Frequent incorrect seating of filter. Read filter manufacturer’s instructions. Train staff in replacing cartridges if necessary. 4 The level of risk will depend on the type, and effectiveness, of any disinfection after cartridge filtration. 5 For example, certification under NSF Standard 53 or AS/NZ 4348:1995.
Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: FILTER NOT REMOVING PARTICLES DOWN TO 2 m IN SIZE – cont’d C1.5.4 Cartridge failure. Regularly replace filter cartridges, and wash pre-filters. Note the date and what is done. Before buying new cartridges check they have certificates showing they meet specifications. Flow rate. Difference between the pressure before the filter and after the filter. (Sudden changes in flow or the pressure difference may indicate filter or pre-filter failure.) Performance certificates. Pressure difference is lower than usual, or flow is higher than usual. Cloudiness in the water following filtration. Customer complaints. Cases of diarrhoea in people drinking the water. Records not kept. Wash the filter cartridge and flush to waste until checks show that particle removal is again effective. Get another batch of cartridges. Consider changing filter supplier. C1.5.5 Contamination of filter housing when changing the cartridge. Disinfect filter housing when installing the cartridge, and flush to waste to remove residual disinfectant. Make sure the person replacing the cartridges knows the correct way to do it to avoid contamination. Test the water leaving the filter for the disinfectant.6 Disinfectant concentration not reduced to an acceptable level. Customer complaints. Cases of diarrhoea in people drinking the water. Continue flushing until the disinfectant cannot be detected. Train staff if necessary. C1.5.6 Flow too high for cartridge design. Keep flow rate less than the maximum the filter can handle. Flow rate. Flow too high. Cloudiness in the water following filtration. Customer complaints. Cases of diarrhoea in people drinking the water. Reduce flow to within specifications. 6 If household bleach (chlorine) is used to disinfect the filter housing, chlorine test tablets from a swimming pool test kit can be used for this. They turn pink when there is chlorine in the water. Use 1 tablet in 10ml of water; a slight pink colour indicates that the chlorine concentration is acceptable.
Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: GROWTH OF GERMS IN THE FILTER Possible hazards: Germs (released from filter into treated water). Level of risk: Moderate C1.6.1 Filter used in the wrong situation or beyond its capacity. Disinfect7 the water before it goes through activated carbon cartridges used to reduce taste problems (including those claiming to stop the growth of bacteria). Regularly replace filter cartridges (especially carbon filters). Note the replacement date. Record filter type used. Check recommended filter lifetime and installation date of cartridge in use. Customer complaints and sickness. Timetable for replacing filters not followed. Avoid using a carbon filter or disinfect the water before it gets to the cartridge. Disinfect water after the filter. Plan when filters have to be replaced, and note replacement dates. UV disinfection Event: UV DOSE TOO LOW Possible hazards: Germs not killed. Level of risk: High8 C1.7.1 Too little UV light passing through the water. Regularly clean the lamp sleeves and light sensor lens. Regularly replace lamp and record the date. Make sure the light sensor is on the wall of the unit farthest from the lamp. Lubricate the lamp seal each time the lamp is removed (use water-based lubricant). Install an alarm that warns when the light intensity is too low and shuts off the water flow. Light intensity. Alarm. Signs of scale on the lamp sleeve and sensor lens. Records of lamp replacement and when sleeves and sensor were cleaned. Alarm triggered (light intensity too low). Water flow shut off. Water inside lamp sleeve (poor seal). No maintenance records. Clean lamp sleeve and sensor lens. Replace lamp. Move sensor so that it measures the light intensity at the wall farthest from the lamp, or buy a unit with a sensor in the right place. Lubricate lamp seal with approved lubricant. Add chlorine to the storage tank until satisfactory water quality can be restored, or close the supply down and arrange for another supply of water. 7 This is best done by adding chlorine to the holding tank. Use 1 teaspoon of bleach per 150L of water in the tank. This gives a chlorine concentration of about 1 mg/L. 8 The quality of the source water and how well other treatment processes before the UV unit work will affect the level of risk.
Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: CONTAMINATION ENTERS THE WATER AFTER TREATMENT – cont’d C1.8.4 Illegal to the water supply. Make sure only properly qualified people make connections to the supply. Inspection of work. Cross-connections found. People who drink the water get sick. Water is discoloured, or tastes or smells bad. Employ a registered plumber to make connections OR make sure the person making the repairs is properly trained. C1.8.5 Contaminants are sucked into the reticulation (“backflow”). Check the reticulation for places where water can be sucked back into the drinking water if the supply pressure drops. Where backflow is possible, make sure that one of the following is installed: backflow-prevention device double check valve air gap. (Some places were these devices may be needed are: swimming pools; stock troughs; boilers; tanks used for preparing agrichemicals; school laboratories.) Check the supply for places where backflow prevention is needed. Check shows there are places where backflow may occur, but there is no device to prevent it occurring. Water is discoloured, or tastes or smells bad. People who drink the water get sick. Install devices to stop backflow where they are needed. C1.8.6 Vandalism or sabotage. Regularly inspect backflow prevention devices, and exposed pipes or valves. Where possible, provide lockable enclosures for parts of the supply that might be intentionally damaged. Check for signs of damage. Signs of damage to a part of the supply. Water is discoloured, or tastes or smells bad. People who drink the water get sick. Repair or replace damaged components. Provide protection to stop future damage.