Sizing your water supply honestly

Every wetting system lives or dies on flow rate, and almost nobody knows theirs. The good news is you can measure it with a nine-litre bucket and a phone timer.

Open the outdoor tap you intend to use fully, and time how long it takes to fill the bucket. Under fifteen seconds is a strong supply. Fifteen to thirty seconds is average and perfectly workable. Over thirty seconds means you are on a low-pressure supply, and you should plan conservatively — fewer nozzles per circuit, and ideally a pump and tank rather than mains.

Two details trip people up. First, test the actual tap you will use, not the kitchen sink; long runs of narrow pipe to a garden tap cost you more than you would expect. Second, test at the time of day you would most likely need the system. On a catastrophic fire day, everyone in the street is running sprinklers, and street pressure drops accordingly.

If your test lands in the high band, the configurator will suggest a Y-type dual outlet so a single tap can feed two protection sets. That halves your plumbing work. If it lands low, you will see a warning instead — not a refusal. The maths still works, but your effective spray radius will be smaller than the nominal figures, so a little overlap is money well spent.

The most reliable setup we see is not the biggest one. It is a modest system fed by a dedicated tank and a petrol pump, because it keeps working when the grid does not.