Break tanks, air gaps and WRAS: what a compliant garden irrigation system needs

Garden irrigation connects your drinking water supply to a pipe that lies in soil, fertiliser and whatever the fox left. The Water Supply (Water Fittings) Regulations 1999 take that seriously, and so do we.

Fluid category 5

The regulations rank the risk of backflow, water flowing the wrong way into the mains, from category 1 (wholesome water) to category 5 (serious health hazard). Buried irrigation, and any irrigation where the outlet can be submerged or in contact with soil, is category 5.

Category 5 protection requires an air gap: the water leaving the mains has to fall through open air into a tank before it goes anywhere near the irrigation pipe. The two arrangements that meet it are a type AA air gap (an unrestricted gap above the tank’s overflow) and a type AB air gap (a gap with a screened overflow). A float valve sitting in the water is not an air gap, even if the tank is labelled as one.

Why a pump means a break tank

Domestic irrigation pumps such as the DAB Esybox range are not permitted to be connected directly to the mains supply. A pump pulling on the mains can draw water backwards through neighbouring fittings; it also breaches the pump maker’s own conditions.

So a pumped system is always: mains, then air gap, then break tank, then pump, then the irrigation. The tank is part of the design, sized for the largest zone’s run, not a bolt-on.

Notification

Installing category 5 backflow protection may need to be notified to the water undertaker, which in most of South West London is Thames Water, before work starts. We handle the notification where it applies.

Electrics

The valves in an irrigation system run on 24 volt AC, which is not notifiable. The pump and the controller’s supply are 230 volt. Any new 230 volt outdoor circuit or socket falls under Part P of the Building Regulations and is installed by a qualified electrician who issues a certificate. Our quotes separate the two so it is clear who does what.

What else a compliant, sensible system includes

• A 130 micron disc filter before the dripline, so it does not clog
• A pressure regulator on drip zones, which want about 1.5 to 1.75 bar
• A master valve, so a leak cannot run all night
• A drain point, so the system can be emptied before the first frost
• A small expansion vessel on pumped systems, to stop the pump cycling on low-flow drip zones

None of these is expensive. All of them are commonly left out.

If you would like a system designed to the regulations rather than around them, book a free visit or read about our irrigation systems.