Whole Site (Zone) and Point of Use Protection

This blog is to help Consultants, Contractors and Installers understand how whole site (zone) protection and point of use protection are used within a building and why they are deemed necessary.


The provision of zone or whole-site backflow protection should be in addition to individual requirements at points of use and within the system”.

Clause G15.25 is the guidance note in the water regulations that mentions these two key statements:

1 Whole site or Zone.

2 Point of Use.


Water Undertaker: The water board, the company responsible for supplying mains water to the boundary of a building or premises.

Fluid Categories: The classification of water and its potential health hazards, there are 5 recognized categories ranging from 1 to 5. With 1 being safe and 5 having the potential to cause serious health problems or possible death.

Potable Water: Water that is classed a wholesome water, or fluid category 1, water that is safe to drink and contains no harmful substances that will cause ill health. Water that the water board will supply to the boundary of the building as above.

Throughout the water regulations the text will refer to “fittings”:

A fitting is simply a device that is used to convey water from the water undertakers supply pipe at the boundary, this will be our pipe, but it also refers to any device used in the building, a tap, a washing machine, a sluice a pump set an outside tap and so on.

Cross Contamination: The risk that fluid from one fitting can mix with the fluid from another fitting.

 Upstream: Flow before a fitting

Downstream: Flow after a fitting

Backflow: Flow upstream that is in a direction contrary to the intended normal direction of flow, within or from a water fitting.

Risk Assessment: Based on the fluid categories above, a fitting will be assessed accordingly, and the correct backflow prevention device will need to be installed.

 The water as delivered to the boundary of our building is completely safe to drink. Under the water regulations, we must not waste, misuse, contaminate, unduly consume or erroneously measure the supplied water. For this blog we are mainly concerned with the contamination element.

Whole Site Protection (Zone)

Going back to clause G15.25 lets look at Zone protection and Whole site protection first. Whole site protection refers to the boundary of our building or the point at which the water undertakers pipe stops, under the water regulations it’s our duty to provide a single check valve or a double check valve at this point. However, this could vary with the severity or risk assessment of the building, generally in a multi-use building the single and double check valve will suffice, remember this is in addition to point of use protection that we will discuss further on. If the building was classed at a higher risk in general, then we may have to consider a RPZ valve (Fluid category 4) device for our whole site protection, still in addition to point of use protection.

Point of Use

For point of use protection, we must consider every fitting individually. We could adopt a very casual attitude in that the water undertakers supply is protected via our whole site device, this could be true. We could fit a fluid category 5 device and be completely safe, but we would not be protecting people within the building from cross contamination.

Every fitting then is risk assessed according to the severity of the water used in the final process, we should consider that a lot of fittings have inbuilt backflow prevention devices and would not need additional equipment. For example, a tap on a basin has an AUK2 airgap by default. A toilet cistern is interposed and is fluid category 5 by default. A washing machine may have a fluid category 3 device built in and so on. However, a bath in a domestic situation is fluid category 3, if the same bath is used in health care or assisted bathing then the risk becomes fluid category 5. The air gap on domestic tap would not suffice in a medical application, the same would apply to our washing machine if it were used in a medical application.

Based on our risk assessment, the correct backflow prevention device is fitted upstream of our fitting, no additional water take-off points must now be fitted downstream of this device.

There may be allowances within our building to further Zone protect rather than Point of use protect. For example, if we have a domestic washing machine and a dish washer in a fluid category 4 situation they must be protected via point of use devices (Figure1).

Figure 1

If we have 2 washing machines that are doing the same job within the building, the water board may allow 1 device to serve both units (Figure 2).

Figure 2


Point of use backflow protection is required, in addition to Whole site or Zone protection, each fitting must be risk assessed accordingly and the correct backflow prevention device fitted.

The water board must be notified of the intended works, this is the duty of the building owner or their appointed representative.

The Water regulations guide is an informative guide with many examples relating to fluid categories and the correct devices required.

Arrow Valves have an extensive knowledge of the water regulations, and an extensive range of products that comply with the regulations and satisfy both Whole Site (Zone) and Point of use protection.