August, 2009
Freshwater is one of the world’s most precious resources. So it’s handy that so much of it falls out of the sky in New Zealand. All we need to do is collect it.
The benefits
Collecting and using rainwater is one of the easiest ways to add a touch of eco-friendly self-reliance to your home and help preserve our environment. And if you are on a metered supply, it will save you money too.
Most areas of New Zealand have a pretty good supply of fresh water, but it’s not always in the right place at the right time. Like the components of any complex long distance supply system, mains water storage dams, pipes, and treatment facilities are costly and come with inherent environmental impacts, including the potential to damage the health of our river ecosystems through excessive extraction and pollution.
The mains system is also susceptible to occasional failures which leave you, or at least your precious vegetable patch, high and dry. This is particularly true in hydro-power areas like Auckland, where in dry periods water and energy authorities have to strike a delicate balance between supplying fresh water and power.
Even small roof water systems can take a huge load off of the mains supply and inspire you to be much more conscious of the water you do use, and how you use it. And they help slow the flow of water in our urban areas, improving storm water management and reducing the risk of flooding
The paperwork
You may need a minor plumbing consent from your council, or a building consent, especially if you are planning anything larger than 25,000 litres. You will also need to fit a backflow prevention device if your tank is being topped up from the mains supply, to keep the two types of water separate.
If you plan to drink roofwater, some councils require you to treat it. Others require an annual inspection of your system. On the plus side, some local authorities offer cash rebates to encourage rainwater use.
Watch out for…
Cleanliness: keep the roof and guttering clear of overhanging branches and regularly inspect and clean them. Consider fitting one of the many guttering filters on the market. The ministry of health recommends disinfecting roof water with small amounts of chlorine, but for those of us who dislike that ‘fresh from the swimming pool’ an ultraviolet light filter system costs about $1,500, plus installment.
Contaminants on the roof: You will need to unplug the system from your roof and find an alternative for a while if you use chemical paints or moss killers up there. Don’t collect from a roof which has lead, chromium or cadmium materials or is unpainted metal. Any paint used should be labelled ‘suitable for potable water supply’.
Your intake: Rainwater is naturally ’soft’ water, meaning it does not contain the dissolved minerals, like chalk, lime, calcium and magnesium mains water in some areas picks up as it percolates through the ground and into our waterways. Getting the right amounts of these minerals is important to our health, so its worth cross-referencing the decision to switch to rainwater with our dietary considerations. This is especially important if we choose a vegetarian or vegan diet, where obtaining the right mineral levels can be more challenging.
Small people: For the same reason, as well as the risk of possible contamination, some doctors advise that even filtered rainwater may not be ideal for pregnancy or for bottle fed babies.
The sums
You only need about five litres of drinking-quality water for each person a day, for cooking, drinking and food preparation. The rest – about 160 litres per person in an average household per day – is used for toilets, showering, washing, the garden, and other uses.
There are many variables, but as a very rough guide each metre of roof space you get hooked up to your system provides around one litre of water in an average year. Even in relatively dry areas, an average home with 120-150m2 provides the potential for at least 100,000 litres of free water each year. A smaller household should get by on a 25,000 litre (5,500 gallon) tank. A larger household may need two.
Metered mains supply of water costs about $1.50 per 1,000 litres, plus a couple of hundred dollars a year for water testing and meter reading. If you are in an area which is not normally metered, you may have to pay $500-$1,000 or more to get one installed. This, plus the cost of your system, suggests a payback time of somewhere around 10 years.
Unless you have a lot of roof, a lot of rain and a plenty of tank space, or you are very frugal with water use, you will probably want to keep a mains back up, to avoid costly water truck deliveries through dry spells.
Tags: green living, water