HIP!: On this site, you will find useful Industry contacts, plumbing gadgets, how to guides, a wide range of plumbing and heating tips and tricks and muchmore to help you make your career a success!

by Steve Tuckwell, technical advisor, The Water Regulations Advisory Scheme (WRAS) Ltd

Hose union taps are designed to have a hose pipe attached, but with use of adaptors it’s possible to connect a hose pipe to most common types of tap. The following information applies to any tap intended to be used with a hose – and applies whether or not the hose is actually attached.

The Water Supply (Water Fittings) Regulations and Scottish Byelaws set out specific requirements for hose taps to prevent backflow.  Backflow occurs when, due either to a supply pressure drop or to a source of back-pressure downstream of the tap, the normal direction of flow is reversed.  Without backflow prevention devices, if the hose end was left submerged, for example in a bucket of cleaning fluid or the garden pond, the contaminated water could be drawn back into the plumbing system and end up in someone’s drinking water.

Hose union taps in houses are typically used for garden watering and washing the car.  In domestic premises, the Regulations require the hose tap to be protected by a backflow device rated to at least fluid category three.  The best way to achieve this is to install a double check valve, located within the building to protect it against damage by freezing (Figure 1).  In use, the hose must not be left lying on the ground or with its end submerged in anything.  The Regulations specify the hose must be hand-held and used with a self-closing flow control – a trigger spray gun.

Figure 1: Domestic hose tap protected by a double check valve

In non-domestic premises the contamination risks are greater, for example industrial processes using toxic chemicals, farms with animal waste and pesticides, mortuaries and hospitals with body fluids.  For these reasons, in all premises apart from domestic ones, the backflow protection required for hose taps is the highest - fluid category five.  This is usually achieved by feeding the tap via a ‘break tank’ - a cistern with a Type AA or AB air gap (Figure 2).

Figure 2: Illustration of fluid category 5 protection for non-domestic hose union tap

A booster pump may be needed to increase the pressure to the tap unless the gravity head is sufficient.  Small combined break tank and booster pump sets are sold as a compact solution to this need.  Ones which are WRAS approved are listed in Section 0230 of the Water Fittings and Materials Directory available on the WRAS website (www.wras.co.uk/directory)

Where water pressure isn’t important, for example filling a tank or bucket, a cheaper way to provide fluid category five protection is by using a Type DC pipe interrupter attached to the tap outlet, with at least 150mm of hose or pipe below it (Figure 3).  No constriction on the outlet is permitted because the backpressure causes water to leak from the air vents.

Figure 3: Correct installation of Type DC device on hose tap.

Further advice and information visit www.wras.co.uk or ring 01495 248454 or email This e-mail address is being protected from spambots. You need JavaScript enabled to view it