disinfect the water (S1.2.1.1–2). (References in parentheses are to the Risk Information Table.) Risk Information 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; MAV – Maximum acceptable value – see DWSNZ:2000; council – regional/district council or unitary authority. Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: EXCREMENT AND CHEMICAL CONTAMINANTS CARRIED ONTO ROOF OR INTO GUTTERING Possible hazards: Germs; herbicides, pesticides, other chemical contaminants that may be airborne. Level of risk: High1 S1.2.1.1 Overgrown trees May cause bird life, possums or rotting vegetation to contaminate the roof catchment area. Water dripping off branches onto the roof may carry Dead animals may fall into the guttering. Tree surgery. Clean out guttering. Provide a grate over the downpipe-gutter connection, or over the whole guttering, to limit entry of vegetation into the tank. Check tree growth at least annually. guttering at least annually. quality directly after rain. Overgrown Dirty guttering. E. coli is detected in 100 ml sample. Tree surgery. Disinfect water in tank or treat with UV at point of use. Disconnect downpipe from tank and clean guttering. Disinfect water in tank (1 mg/L of chlorine for clean water,* possibly up to 5 mg/L if water is poor quality) or treat with UV at point of use.
S1.2.1.4 Contamination of roof and guttering during spraying to protect roof timbers against and other insects, or proofing against spiders. Ensure that the contractor is that the roof is used to collect drinking-water, and that overspraying must be avoided. Obtain a guarantee from the contractor that persistent organochlorine pesticides will not be used. Nature of pesticides used by contractors. Pesticides in water following treatment of roof timbers, if there is concern about the nature of the pesticides used, and the way in which they were used. Use of persistent insecticides by contractor. Knowledge of overspraying events. Water contains pesticides at more than 50% of their MAV.2 Use different contractor. Use first-flush diverted or disconnect downpipe, before first rain after treatment of the roof. Decontaminate the roof. Use alternative supply until decontamination is complete. 2 The risk associated with this will depend on location within the country. Causes Preventive measures Checking preventive measures Corrective action What to check that action is needed Event: EXCREMENT AND CHEMICAL CONTAMINANTS CARRIED ONTO ROOF OR INTO GUTTERING cont’d S1.2.1.5 Vandalism/ sabotage. Ensure access to the roof is made as difficult as possible, by removing such things as ladders. Inspect the roof regularly for deliberately introduced contaminant sources (eg, bags of chemicals). Check the roof for unexpected objects on it, and the area surrounding the building for objects that may make access to the roof easier. Evidence of unauthorised access having been gained to the roof. Eliminate means by which access to the roof was gained. Remove contaminant source, disconnect downpipe and wash down. Event: MATERIALS DISSOLVED FROM THE ROOF, FLASHING GUTTERING AND DOWNPIPES BY THE RAINWATER Possible hazards: Heavy metals (lead, copper, chromium, cadmium). Level of risk: Moderate
S1.2.2.1 Lead-containing materials (paint, nails or flashing) used in roof construction; guttering constructed from corrodible material (eg, copper). Use lead-free materials on the roof (paints, flashings, Keep roof surface well maintained. Use plastic guttering. Inspect condition of the roof surface at least annually. Test for heavy metals in roof paint (one-off test probably sufficient). Heavy metals in the water if there is a likely source of them on the roof. Roof surface in poor condition and needs repainting or replacing. Leaded paint test on roof paint is positive. Heavy metal in the water are more than 50% of their MAV. Cases of lead (or other heavy metal) poisoning, but be aware that such cases may have other causes. Replace inappropriate materials. Repaint roof, or replace roof. Replace guttering. Event: CONTAMINATION OF THE WATER WHILE IN THE STORAGE TANK Possible hazards: Germs; plasticisers (di (2-ethylhexyl) phthalate), possible reduced disinfection efficacy by chlorine because of high pH. Level of risk: High S1.2.3.1 Animal or human access to storage tank (see S1.2.3.5). Ensure the storage is covered. Install mesh on vents, overflow, etc. Undertake regular tank inspections (monthly). For wooden install metal band around wooden tanks to prevent animal access from ground level remove vegetation near tanks install internal liner for tank roof. Monthly tank inspection. quality. E. coli is detected in 100 ml sample. Dead animals in tank. Mesh/grills disturbed by animals to get access. Unpleasant taste and odour. Water turbid. Disinfect tank (1 mg/L of chlorine for water, possibly up to 5 mg/L if water is poor quality) depending on water quality. Replace or provide mesh where necessary. Prepare tank inspection schedule.
S1.2.3.2 Accumulation of sediment in tank. Undertake regular (annual) cleaning of tank. Use two storage tanks, the first feeding into the second, and draw water from the second (this reduces sediment being carried through into the reticulation). Monthly tank inspection. quality. E. coli is detected in 100 ml sample. Dead animals in tank. Mesh/grills disturbed by animals to get access. Unpleasant taste and odour. Water turbid. Instigate inspection and cleaning programme. Install a second tank. S1.2.3.3 Water stagnant in plastic tank for too long. Ensure the material chosen for the tank is suitable for drinking-water purposes. Locate tank in a shaded area. Position into the tank near the bottom to ensure good mixing and avoid stagnant zones near the tank bottom. Taste. Sample for phthalates (plasticisers). Plastic taste. Di phthalate is more then 50% of its MAV2. Reduce tank size for faster turnaround of water. Flush tank a number of times on first filling. Relocate tank to area that is cooler. Relocate inlet to tank. S1.2.3.4 Dissolution of lime from new concrete tank (this problem should reduce as the tank ages). Line the tank. Increase buffering capacity of the (eg, addition of sodium bicarbonate). pH. pH above the guideline range (7.08.5). Add sodium bicarbonate until pH reaches an acceptable level. Event: CONTAMINATION OF THE WATER WHILE IN THE STORAGE TANK cont’d S1.2.3.5 Vandalism/ sabotage. Restrict access to tanks (fences, locked hatches). Regular inspection of tanks for evidence of unauthorised access. Evidence of unauthorised access having been gained to the tank. Fence tank, or provide lockable hatches. Event: VOLCANIC ASH FALL ON ROOF2 Possible hazards: Arsenic, fluoride, and metals. Level of risk: Low