Sustainable Water

By Graham Hepburn

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
million tonnes of water a day in the steel making process but this is constantly recycled – cleaned,  cooled and recirculated - so that only 1% of it is discharged and what is discharged is clean enough to
drink.

Homeowners collecting drinking water and greywater replacement from metal roofs can do so knowing they are harvesting a renewable resource. Metal is the roofing material that is arguably the best suited material for rainwater collection.

Metrotile have provided a solution that an increasing number of home owners have with shingle products
installed in and around the 1980’s. Whilst the original unit’s unique design was complimented by the low, flat profile of shingles the long term performance was questionable. In this instance the owners of three units have approached the solution in two ways. One has decided to re-coat the existing Hardie shingles to extend their weatherproofing and visual appearance whilst the other two have chosen to replace the entire roof with Metrotile Shingles. The centre unit was the first to be re-roofed and the owner of the third unit was so impressed by the result he elected to use the same Metrotile Shingle. This made good sense and enhanced the overall visual appeal of the collective group of units.

The original roof was showing serious delamination which did not reflect the well maintained appearance of the units and the owner was no longer confident that it would remain watertight in the near future.

Several factors influence the decision to use Metrotile Shingles the first being they had to compliment the original design with the low profile. The Metrotile Shingles have a natural stone textured finish that also had an appeal as the glare from the original shingles was a problem and one which is often overlooked. Many roofs reflect light which can have an adverse effect on neighbouring homes in the area.

Maintenance and longevity was also a priority and a concern for those who are not able to crawl around the
roof cleaning and maintaining it. The Metrotile 50 year pro-rata Weather Proof warranty and 20 year pro-rata Surface Coating Warranty was an added bonus which helped to validate the owner’s decision. “I  understand Metrotile have a very solid history and they stand by their product. To be honest I expect this from any NZ manufacturer,” says the owner.

Above; The original Hardie Shingles that were stripped from the roof.
Centre: The original Hardie Shingles that have been recoated.
Below :the New Metrotile Shingle roof.

Whilst not needing to collect potable water from the roof the Homeowner was interested to hear that potable water could be collected from the Metrotile Shingle roof, which is not the case with all light weight shingle substrates, some of which include or have historically included bitumen and asbestos in the manufacturing process. There is an increasing environmental awareness of harvesting water rather than wasting it and in many instances having the choice is important to home owners.

The Metrotile Shingle profile is unique in the market and the lowest profile pressed metal shingle available. To match the neighbours roof clearly meant dealing with one of Metrotile’s certified distributors and being a sensible Kiwi the owner obtained 3 quotes before settling on Roof Improvements to undertake the task of stripping and re cladding the roof.

Roof Improvements are an independent specialist roofing company who are based in Takanini and service the Greater Auckland market with longrun and metal tiles. They have been in business for over ten years, with the owner and many of the staff having over 25 years experience in roofing.

“These boys have done a great job and I am very happy with the result. There was little disruption, they cleaned up and the entire job was done in 3 days. I questioned one flashing and it was rectified immediately with no fuss or argument. A great team I am happy to recommend to anyone. “says the owner.

The stripping and re-roof on this project presented no structural issues as the ply base, that the Harvey Shingles were attached to, was in good condition. Building paper was laid and the Metrotile Shingles were screwed directly onto the ply. The finished result looks stunning and as on many new and existing projects throughout the country the unique Metrotile Shingle gives the low flat profile that so many home owners and designers strive to achieve. The benefits; low maintenance, looks great, a range of natural colours,