A Farmer who receives grant aid under the new Rainwater Harvesting Scheme will have to comply with a Department of Agriculture Specification now being written for the scheme.
Design of Systems
A rainwater harvesting system involves collection, filtering and storage of rainwater. Further treatment of the collected rainwater is necessary to make it potable and, therefore, suitable as drinking water for lactating dairy cows and for washing milking machines, bulk tanks, etc. This further treatment is optional under the new grant scheme.
Only rainwater from roofs can be harvested i.e. rainwater cant be harvested from yard areas. Rainwater may be collected from tiled, metal and fibre cement roofs but not from asbestos-cement roofs.
Tanks may be constructed of conrete, steel, plastic or GRP. Above ground tanks will have to be insulated and opaque to minimise the potential problems of freezing, warming and algal blooms.
- Under the scheme rules, all tanks will require a solid cover and screened ventilation to prevent entry of dirt.
- Tanks will require a calmed inlet to prevent the disturbance of any sediment at the bottom. Where feasible, a floating extraction point from the tank will have to be used, approximately 100mm below the surface of the water. Otherwise, a fixed extraction point may be used, 150mm to 200mm above base.
- Where more than one tank is used, the pipework connection must ensure through-flow of water to avoid stagnation.
- Where mains water is fitted to the tank as back up, there must be back flow protection.
- Tanks will have to be fitted with an overflow outlet attached to a suitable clean water drainage system.
The capacity of the rainwater harvesting tank will have to be sufficient to hold between seven days and 18 days rainfall from the collection area. The capacity will be calculated from the average annual rainfall, the size of the collection area and the demand on the harvested water.
Rainwater Harvesting systems will require proprietary self cleaning filters to remove leaves, moss, etc.
Where used, UV treatment systems and chlorination treatment systems will have to be sized, installed and maintained in accordance with the manufacturers recommendations.
Rainwater must be collected by leak proof gutters/valleys and fed thorugh downpipes into piped drains. Drains will bring harvested rainwater to the storage tank. Where an overground tank is used; a sump will be constructed to hold a pump that will transfer the rainwater in to the storage tank.