The use of mains water in England and Wales is regulated by the Water Supply (Water Fittings) Regulations 1999, an Act of Parliament which lays down what can and cannot be done with drinking (potable) water supplied by the water companies. The Act contains two important principles: water should not be wasted and water should not be contaminated.
In order to comply with the first principle, it is important that the water provider is contacted before an irrigation system is installed, with information on what system is being proposed.
To comply with the second principle, all irrigation systems must have some means of back-flow prevention. Depending on how the water is used, the law assigns a risk category from 1-5. Category 3 allows use of fixed head sprinkler systems with the sprinkler heads no less than 150mm above the ground level. When using hoses, or any other irrigation nozzle located below 150mm, then the risk category is category 5.
For irrigation systems which fall into category 3, a ‘Type EC’ verifiable double check valve or ‘Type ED’ non-verifiable double check valve is sufficient protection. This needs to be fitted into the pipework and protected from frost.
For irrigation system in category 5, such as dripline and sprinklers below 150mm, a ‘Type A’ airgap is normally required. Most domestic cold water tanks have a ‘Type B’ arrangement, so it is important to ensure the break tank is designed for irrigation. ‘Type A’ airgaps consist of an inlet valve which is positioned above the highest possible water level of the tank. This eliminates any possibility of the inlet valve being submerged, and water from the tank being drawn back into the mains water supply. With a ‘Type AA’ airgap, the rim of the tank forms an overflow and the inlet valve is positioned above the tank rim. With a ‘Type AB’, a large overflow weir is cut into the side of the tank to prevent the water level reaching the inlet valve.
As ‘Type A’ airgaps result in the mains water pressure being lost, a pump is then needed to re-pressurise the water supply. Vertical or horizontal electric pumps are normally used for this purpose, normally under the control of an irrigation timer or an auto-start device.
Access Irrigation can supply compliant water storage tanks, and also produce a range of pressure booster units which combine a break tank with a pressure booster set.
Note: If the irrigation system is to be installed in a private, single occupancy dwelling (referred to as a ‘Domestic’ or ‘House Garden’ in the regulations) then there are slightly less stringent rules apply – see blog post ‘Water Regulations for Domestic Gardens’.