Minimum Flow Rate and Water Pressure at a house?

1 Mar 2011
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West Glamorgan
United Kingdom

What is the minimum flow rate and water pressure that should be delivered to a property.

On my kitchen tap I am getting about 8-10 litres per minute and on the outside tap I am getting 3.5 bar according to the plumber who said that my water pressure is very good, although I am unconvinced.

I have had the stop tap in the street replaced and the run from there to the mains in the road by the water board but it has done little difference to the water pressure.

I have also had the internal stop tap replaced as this was about 60 years old and was seizing and leaking but there is still a leak coming from the black alkathene pipe as it enters the stop tap. Which several plumbers have been unable to fix.

When looking at the old stop tap and part of the alkathene pipe that was cut away the alkathene was very thick more like a brittle rubber and the internal diameter of the pipe was very small much less than 15mm.

The water board has said that I have black alkathene to copper back to alkathene in my ground before it enters my property

Could the small internal diameter of the black alkathene pipe that is causing the poor flow and water rate pressure and would a new water supply into my property be the best option?
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You need to read the FAQ on this site and any other search so that you can understand the relationship between pressure and flow!

Its a little vague and different figures are sometimes given, but water suppliers seem to suggest that they have to provide a minimum static pressure of 0.6 bar and an open pipe flow rate of 6 litres per minute.

But that's only at ground level!

On a third floor of an apartment building the pressure can be nil !

If you have a static pressure of 3.5 bar then you're on to a winner and a new pipe from the external stopcock into your house should sort you out.

Wish I had 3.5 bar static...we're barely at 1 bar in my new place and can't turn on another tap when the electric shower is running as the shower cuts out.

As for the leak into the internal stopcock, it sounds like you've had a bad run of plumbers. They need to fit a Philmac plastic stopcock, that'll cure it. Might need a couple of wraps of PTFE if the pipe is scratched

So what does 3.5 bar static mean? and how would having a new water supply pipe from the external stopcock into my house help?

Would this improve the flow rate?

By the looks of things I have a new Philmac plastic compression fitting between the alkathene and the new stopcock
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in round figures, 1 bar is the pressure you get from a tank of water that it 10 metres above you. It's enough to fill most loft tanks, and gives a fair shower if flow is reasonable.

Larger diameter pipes, and stopcocks, will obstruct the flow less so that the water comes out faster. Stylish imported taps may also restrict the flow rather more than traditional British designs.

Look out for any stopcocks, service valves and flexible braided tap connectors, which will all restrict flow.

A photo of your stopcock and pipe may help (put a 50p piece on it to show scale).

Modern plastic pipe is usually blue, and a metric size, e.g. 20mm. Black Alkathene is usually an Imperial size, e.g. 3/4", so possibly a metric fitting has been used and is a poor fit. Sometimes identification is visible, printed on the side of the pipe.
The problem is my alkathene pipe is very brittle and too thick in diameter the actual hole is less than 3/4 its more like microbore that is used as my main water supply.

Is this why

1. My water flow is so poor at the house
2. Is it recommended to get a new water supply into the property?
SW Water only have a minimum supply pressure not a maximum as I found out when, following a number of leaks, I measured the incoming water pressure at over 12bar (~ 180psig)!!! They seemed mildly perplexed to have a complaint about high pressure.

SWW, and I suspect many others, take no responsibilty for any leaks caused by 'high pressure'. They did supply a pressure reducing valve FOC albeit for me to get installed and without accepting any responsibilty for any damage caused by high pressure.

It's 12bar because it comes straight off a 12" trunk main in the road with no intermediate distribution pipework and its associated pressure losses..

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