20 Nov 2014

Rain Water Harvesting

From Our Changing World, 9:34 pm on 20 November 2014

By Alison Ballance

Stan Abbott stands next to the Roof Water Research Centre on the roof of Massey University in Wellington, which comprises 16 large water tanks and a sophisticated weather monitoring system.

The Roof Water Research Centre on the roof of Massey University in Wellington comprises 16 large water tanks and a sophisticated weather monitoring system. Photo: RNZ / Alison Ballance

The Roof Water Research Centre at Massey University in Wellington is run by microbiologist Stan Abbott. Stan is an enthusiastic advocate for collecting rain water from roofs in both urban and rural situations, yet he’s also aware of potential contamination from seabird droppings and wind borne pollutants. He says that although very few people who report gastrointestinal problems believe they drank contaminated water, he believes that regular drinkers may be immune, and also that a Food Safety Authority study showed that there is significant under-reporting of illness related to tank water.

Ten percent of New Zealand households already rely on rain water collected from the roof as their primary water source. These houses are mostly on farms and life style blocks, as well as in isolated areas such Waiheke Island. However, some District Councils such as Kapiti have passed by-laws so that all new dwellings must have a 10,000 litre rain water tank or a 4,000 litre rain water tank and a grey water diversion system. Stan believes that more urban dwellings should collect water for non-potable purposes such as flushing toilets and watering gardens.

Stan also believes all households should have a small rainwater tank for use in emergency situations such as after a large earthquake, when municipal water supplies may be interrupted for a period of time. Modelling by GNS Science showed that following a significant rupture of the Wellington fault, Wellington city might be without mains water for 35-55 days. Stan stresses this emergency rain water should be boiled or treated before drinking.

Stan Abbott led a study looking at water quality in tank water samples from 560 private dwellings in New Zealand. At least half of the samples exceeded minimal acceptable levels for contamination, and more than 30% of samples showed evidence of heavy faecal contamination.

Further research into various physical methods for collecting clean roof water showed that a first flush diverter was the single most effective way of maintaining good water quality. The first flush diverter diverts the first 50 to 100 litres of water collected during a rain event, ensuring that contaminants don’t make it into the tank. Other features such as a calmed inlet ensure that sediment in the bottom of the tank is not stirred up, while down-pipe rain-heads ensure that debris such as leaves doesn’t wash into the tank.

The Roof Water Research Centre has a farm of 16 large rainwater tanks on the roof of Massey University in Wellington, and a sophisticated set of sensors that allow Stan to correlate microbial contamination with particular weather conditions and water temperature. Stan uses the Colilert system to test for E. coli, which is an indicator of faecal contamination.