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Water Flow Rates - Finding

How to Find Your Water Flow Rate

This is not as easy as one might expect. There are rarely any hard and fast estimates of the water flow rate in any particular building.

Don't be misled by "Bar" readings.

Bar eg "3 Bar"... or "6 Bar" refers to static pressure. This is not your flow rate. 

(Flow rate is "Dynamic pressure").

To size your water filter correctly you need to find your flow rate not your static water pressure.

Even a plumber or engineer would only be guessing your water flow rate. They would have to work it out on a case-by-case basis.

(If you want to get technical; they would calculate velocity - from the Bar pressure - by the tube size).

The Good News

Provided you are prepared to roll up your sleeves for a few minutes, it is not that hard to get a fairly accurate estimate of the flow rate in your house.

The best way of doing this is to actually get a bucket and stopwatch and time the flow from each tap or shower head. This might seem silly but it will be accurate.

The trick is to estimate the maximum amount of water you might use at any one time. That will be your maximum flow rate aka "peak flow rate".


Flow Rate Considerations

There are various factors to bear in mind.

For example, your water heater may only allow one hot supply at a time.

So whereas you might have three bathrooms, actually only one can be used to run a bath or a shower at one time.

Power showers can do 40 to 50 Litres per minute.

Toilets might flush several gallons but these come from the toilet's cistern/tank which then fills up slowly.

A cold water tap turned on fully and running vigorously enough to throw small splashes out for several feet is running at about 17 L / min.

Pump / water pressures and flow rates

Don't be tricked by the reported pressure of your mains water or your borehole or well water pump - if you have a private water supply. (See "Static Pressure" / Bar measurements above).

Just because a pump can work up to a certain rate does not mean that is the flow coming into your house. This is set by the amount of water you are using in the house at any given time.

Put simply the water only flows when you turn on your taps. The number of taps you have on at any one time is what will affect your flow rate.


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