The LWF Blog

Fire Safety Engineering for Design – Sprinkler – Water supplies – Part 254

September 29, 2025 9:00 am

LWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 253, LWF began to discuss the water supply for a fire suppression/sprinkler system. In part 254, we continue to look at the water supplies for sprinkler systems, starting with duplicate supplies.

A duplicate supply of water for a sprinkler system is precisely what the name suggests and may comprise a combination of water supply sources. In the UK, this tends to be a full holding capacity water storage tank and duplicate fire pumps.

Where duplicate pumps are used, each pump must be capable of satisfying the requirements alone, providing a level of resilience. Where two electric pumps are provided, independent electric supplies should be in place for each pump, in case of failure of the first electrical supply. Commonly, duplicate pumps are powered by differently, e.g. electric and diesel.  Where the capacity is too great for a single pump to fulfil the requirements, three pumps may be used, each of which can provide half of the required capacity.

In some instances, the difference in height between the highest and lowest placed sprinklers may exceed 45 metres. This type of system is classed as ‘high-rise’ in the UK. The resulting system should be subdivided into sections, each having a highest to lowest differential of not more than 45 metres.

Each section of the sprinkler system should be fed from a separate set of pumps or from separate stages of a multi-stage pump. However, each section may be fed from a common water supply, provided it is capable of fulfilling the highest possible demand on the system.

In cases where the pipes have been hydraulically calculated, the resulting flow/pressure characteristics of the pumps and size of the storage tanks are based on the hydraulic calculation.

The calculations for most and least favourable locations should be plotted on a graph using a linear scale for pressure and a square-law scale for flow. The resulting system demand curves should appear as practically straight lines on the graph.

Then, the design site performance curve for the pump, with the tank full and with the tank at its lowest operational level, should both be plotted onto the same graph. The installation demand points should be covered by the pump curve when the tank water is at its lowest level so the design flow rate is available through to the end of the period of operation.

In part 254 of LWF’s series on fire engineering we will continue to talk about duplicate supplies and how to ensure your sprinkler system has sufficient water for any foreseen eventuality. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.

Lawrence Webster Forrest has been working with their clients since 1986 to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact the LWF office on 0800 410 1130.

While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.