Rain Water Tanks
Rain Water Tanks
Collection of rainwater for drinking and household use is common in Northland, especially in more rural settings. Rainwater is relatively safe to drink, however it is very important to collect and store this water correctly in order to minimise the risk of contamination.
Possible source of contamination could include animal or human faeces entering the source of supply, lead flashings and lead-based paint products causing elevated lead levels in collected water, bird, possum or other animal droppings, agrichemical spray drifts landing on roof and flushed into tanks with first rains and the decomposition of leaves can also cause taste or odour issues.
Tips for Roof Water and Tanks
Below are some points which can help reduce possibilities of contamination.
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Install a first flush diverter. This is a very important device that flushes to waste the first 50 - 150 litres of water depending on your roof area. The first runoff usually contains the majority of contaminants, especially after long dry spells.
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Use plastic pipes
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Use safe roof paint - not lead based
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Avoid placing TV aerials and other antennae on roof for birds to perch on
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Avoid planting trees beside the house
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The storage tank should be covered to prevent further contamination from animals and birds in order to minimise evaporation losses
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A two tank system is better than one large tank, as the first tank can be used primarily as a settling tank with the second tank being the draw off.
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Try and avoid piping design that has long sections of pipe that will contain standing water before the tank. During hot dry spells anaerobic decomposition of organic matter contained within the water can occur and it will be forced into the tank following the next rain. Anaerobic decomposition often causes strong taste and odour issues due to hydrogen sulphide build up and other by-products.
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Rain water is usually slightly acidic with a pH <7. Water stored in concrete tanks often has a pH >7 due to calcium carbonate leaching from the cement. Plastic tanks are inert and will not alter the pH. Sometimes a blue staining will occur in baths and showers due to a chemical reaction in the copper piping and hot water cylinder. This can be overcome by various methods such as placing concrete bricks or marble chips in the tank which raises the pH of the water.
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There are many different types of water filters on the market which offer various levels of protection depending on cost.
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Clean and disinfect the system every 6-12 months including the guttering. This may include opening the scour valve on the tank to remove any accumulated sludge. Disinfection can be achieved by calculating 167ml of household bleach per 1000 litres of water (167ml= 2/3 cup). Leave it in the tank for a few hours before flushing to waste.
Water Testing
There are a number of private services around the district that offer water testing if you suspect that your tank water may be contaminated. The only water testing laboratory in the District accredited by the Ministry of Health is Transfield Services Ltd which are also the Councils maintenance and operations contractors.
What if my water tanks runs out of water?
As water tanks are privately owned, Council has no involvement in this and you will need to buy your own water to refill your tank.
Water Suppliers
If you run out of water there are a number of bulk water carriers registered to use a FNDC filling point that may deliver drinking water in your area. This is not a Council service and FNDC does not take any responsibility for the quality of water once it leaves the filling station point. View a list of FNDC Registered Water Carriers in the district.
Page created/updated: 11 December 2009 at 9:42 am
