Rainwater Harvesting Domestic, Agricultural and School Applications

In 2005, Technological University Dublin (DIT) School of Civil and Building Services Engineering was commissioned by the National Rural Water Monitoring Committee (NRWMC) to investigate the feasibility of supplementing treated mains water used for non-potable purposes (NFGWS, 2008). This project involved the design, installation, commissioning and monitoring of rainwater harvesting (RWH) facilities in a domestic housing development and in an agricultural setting. A second study commenced in 2008 when DIT was commissioned by the Department of Environment, Heritage and Local Government (DOEHLG) to monitor water use and assess the efficiency of rainwater harvesting facilities installed in a primary national school. Daily / monthly rainfall, water demand, mains top-up were monitored and analysed for the domestic, agricultural and school sites. The Efficiency ratio (ET), Storage fraction (Sf), Demand fraction (Df), Overflow fraction (Of) were calculated for the three rainwater harvesting systems (RWH). An economic model was developed to calculate cost of producing one m³ of water using RWH , compare the Net Present Value (NPV) cost of RWH water supply versus mains water supply and to illustrate the preferred scenarios in Ireland under which RWH is economical viable. These include; Storage designed for no greater than 90% efficiency, capital grant allowance of minimum 30% coupled with a 50% reduction for householders with RWH. The cost of mains water per m3 is similarly priced as harvested rainwater per m3. In this study this equates to €8 per m3 A 20% reduction in free allowances to the householder coupled with a 50% reduction for householders with RWH