Rain water harvesting in urban New Zealand

Rainwater harvesting is a practice already widely used throughout rural New-Zealand, which makes it well developed on the country’s market as well as in people’s minds. Therefore, it is pertinent to study whether this sustainable practice could be implemented in urban areas so as to provide water for purposes such as toilet flushing, washing machines and garden use. This study concentrates on the health issues posed by roof water collecting with qualitative results for water quality, and on other aspects such as costs and benefits of such systems, politics towards this practice, and the impact it can have in recovering from a natural disaster. The results showed both environmental and faecal contamination of the harvested rainwater especially after important rainfall events, and the presence of such contamination in stored water can lead to disease outbreaks especially if consumed. However, testing effectuated on first flush diverted volumes revealed that such devices can considerably improve the harvested water’s quality if a quantity of water between fifty and eighty litres is diverted at the beginning of heavy rainfall. Cost wise, the slimline tanks series is well adapted to urban environments due to their shape but the price to pay is twice that of a normal tank. A 5’000 litres normal tank seems the best option as its mean price is of 1’500 NZD and its efficiency in providing the household with water for different uses is usually around 80% and can reach up to 95%. Furthermore, if in the future the authorities realize the advantages of having rainwater tanks installed in urban areas, rebates could then be offered on the acquirement of such systems.