Sustainable Water

There’s little doubt that water is one of the planet’s most valuable commodities and maintaining water supply will become even more important if predictions about the dire consequences of global warming become true.

If the planet is going to be subjected to the extremes of flooding and drought, then security of good quality water supply will be increasingly important.

In rural areas with no mains supply there has been little choice but to harvest rainwater from roofs and collect it in tanks, and many rural households prefer this source, but in recent years suburban dwellers and even businesses have begun to get in on the act.

This trend is partly due to greater environmental awareness but also to the fact that water is becoming an increasingly expensive commodity. Councils have also been encouraging home owners and businesses –  sometimes with financial incentives - to collect rainwater because this has twin advantages: it helps to reduce stormwater flows and alleviates some of the pressure on water supply and water infrastructure from a growing population.

In urban environments with their proliferation of impermeable surfaces, stormwater during heavy downpours can cause surface flooding and overwhelm sewers, causing foulwater discharge into waterways. Collecting water off roofs reduces stormwater problems by attenuating the flood peak and helps to conserve a valuable resource and will reduce the need for councils to build more dams or find other water sources. If you are providing your own water, then that also cuts demands on treatment facilities and pumping stations, which in turn means they will need to consume less energy. In urban Australia new houses are required to have stormwater retention systems for these reasons and this has encouraged use of the retained water in tanks for non potable uses, often metal tanks are the most cost effective due to the easy ability to have a non-circular tank.

Just harvesting rainwater for uses other than drinking drastically cuts demand on mains supply. The old Waitakere City Council estimated that only 5 litres per person per day is needed for cooking and drinking while 150 litres per day is used for bathing, washing dishes and clothes, flushing toilets, in the garden or for washing down cars etc. As New Zealanders have known for decades, catching water off a metal roof for drinking and other household uses is easy and safe as long as some basic precautions are taken.

BRANZ says metal roofs are safe to collect rainwater from but a check should be made to ensure there is no lead, chromium or cadmium in the roof and its flashings or in any soldering or paint. The roof and gutters need to be cleaned regularly with diverters in place to make sure contaminants such as bird droppings that are being washed away aren’t entering the water supply. And a first-flush diverter and debris diverters should be installed – this reduces the risk of contaminants entering the storage.

Pacific Coil Coaters and New Zealand Steel have tested the painting systems for the potential to release contaminants and have shown that there are no contaminants released of any public health concern. Therefore, excluding other environmental factors, when you use COLORSTEEL® or Colorcote® pre-painted metal roofs for the harvesting of rainwater, you can rest assured that the product you are using will not contaminate the water.

The Virginia Rainwater Harvesting Manual recommends metal and membrane roofs, with the exception of copper and lead. It does not recommend asphalt or wood shingles, or tiles made of concrete or terracotta. The reasons for the preference of metal roofs include a lesser content of arsenic, copper, mercury, cadmium and lead contaminants, Uneven surfaces as in asphalt or wooden shingles also contribute to a greater opportunity for algae and biological growth and thus a greater risk of bacterial contamination of water collected. The manual cites Zincalume® and Colorbond® as roofs designed for rainwater harvesting. Colorbond® is similar to the prepainted material supplied in New Zealand by New Zealand Steel (COLORSTEEL®) and Pacific Coil Coaters (Colorcote®). These New Zealand products are arguably the best materials in the market for rainwater harvesting enabling the augmentation of our water resources, which are only becoming more stressed and are critical to the survival of the human race.

Roll-forming of metal for roofing uses no water and the manufacture of the steel coil from which metal roofing is made uses minimal water. As an example, New Zealand Steel’s plant at Glenbrook uses about 1