Water mains pressure and flowrate

[akistzortzis]

Hello everyone,

I am writing here because I found a very similar thread back in 2017.

The water company carried out major works in my small street of 13 houses, replaced the water main, I am not sure what with. They dug up to my water meter and I presume replaced the mains pipe right up to it.

From the water meter there is an underground, 40+ year old water pipe, black, seems to be around 20mm OD and perhaps 15mm (or less) ID. It runs for about 40 meters before entering the house.

I have just measured around 2.6-2.8 bar static pressure and around 15lt/min flowrate. With the tap fully open the water pressure collapses, almost to 0. In practice, if I flush the toilet, there is a trickle coming out of the water tap in the bathroom. Or if someone is having a shower there is very, very little water at the kitchen tap.

We are digging a trench to install a new electricity and gas lines, and at the same time I'd like to replace the old mains water pipe as well.

What size should I go for, and is it likely to make a difference? Choices are 25mm, 32mm, 50mm, 63mm, 90mm. The 32mm is 26mm ID, the 50mm is 40.8mm ID, the 25mm is 20.4mm ID and finally the 20mm is 15mm ID. There are differences in price especially as I might just need over 50m, otherwise I think I'd use a large size eg 50mm.

Any comments welcome.

 

[RJC]

I think around 25mm is the norm for supply to houses, I used this when changed my mains supply. Was old galvanized pipe

Who will connect it up to the stop valve on the street.

https://www.screwfix.com/p/mdpe-pipe-blue-25mm-x-50m/19606

 

[Pho]

The offtake from the water main to your house is usually 32mm SDR 11 (26mm ID) MDPE.

At least for a 40m run you can get away with buying a 50m coil and running it as one continuous piece, you don't want to be putting push-fit fittings in under your drive. If you do need to join it where it's not accessible and will be guaranteed to last as long as the pipe you want to use electrofusion fittings.

 

[JRJ]

When I was sorting out the mains water on our project I dug out the old connection which was 15mm copper and found that the water board had replaced the mains at some point and installed new stop taps which had a 12" length of 25mm MDPE before stepping down to the 15mm copper, made life much easier as I just changed out the connection to a 25mm-25mm and ran the new pipe in 25mm to the internal stop tap, now getting just short of 6 bar static pressure and 20+ lt/min flow.

 

[akistzortzis]

Yeah I do not think I can do anything about static pressure, being at 2.6-2.8 bar, but I may be able to improve on flowrate or dynamic pressure, currently if I turn the tap on my pressure drops to almost 0. I hope a larger diameter pipe will help with this.

The first leg of the run is 35 meters (to the annexe) and from there the second leg is another 30 meters (to the main house). I am thinking of installing two separate runs or a single larger diameter, currently looking at 50mm.

 

[JRJ]

Have a dig around your stop valve and see if you can see where the new meets the old, I only went with 25mm as that's what I had coming off my stop valve if I'd wanted bigger then it would have been a costly process through the water board to get the mains upgraded, as it is we need to fit a pressure reducing valve in the boiler room.

 

[BigBoy]

Yeah I do not think I can do anything about static pressure, being at 2.6-2.8 bar, but I may be able to improve on flowrate or dynamic pressure, currently if I turn the tap on my pressure drops to almost 0. I hope a larger diameter pipe will help with this.

The first leg of the run is 35 meters (to the annexe) and from there the second leg is another 30 meters (to the main house). I am thinking of installing two separate runs or a single larger diameter, currently looking at 50mm.

You have a larger issue rid your pressure drops that low, I would suggest you talk to your provider and see if they can help.

How old is the incoming mains pipe, is it lead or plastic, do you suffer with lime scale?

**After re reading the thread get your supplier to upgrade your incoming supply, at 40+ years old the inner diameter is probably half of what it should be!

 

[Terminal_Boy]

Get you water provider round to measure pressure and flow both sides of the water meter if works have been carried out upstream from you.

Some months ago, my water provider put in some additional irrigation points for a neighbouring farmer and we had 2-3 days of hyper aerated followed by a lack of flow. They sent a technician out who demonstrated good flow 30l/min plus and 7-10 Bar on their side of the water meter. He inspected the ancient pressure reducing valve and filter on our side which corroded solid and told us they needed replacing.

I replaced the PRV and filter on our side and the flow on our side of the meter was vastly improved, but not as good as it had been, especially when a garden hose was in use. Finally got the provider to send another technician out after Lockdown eased who again showed good flow and pressure on their side of the meter. I showed him pressure dropping off at the nearest hose and he disconnected the meter to inspect it.

Intake side of the meter was utterly jammed with fibrous debris and he was surprised that we had any flow at all. New meter was fitted and we now have excellent pressure and flow across the property.

TLR - Get your water supplier to check flow at the output of their meter. If it’s poor there, it’s their problem.

 

[Michael C]

I have a similar issue to OP, really hoping someone can shed some light.

Our house is ex-council, built in 1936 and our water service pipe is lead and there are 4 houses between us & the outside stop valve (not even on our road ).

Static pressure is 2.2 - 2.5 bar and the flow rate seems OK, I don’t have a meter but I filled a 7 liter bucket in just under 30 seconds so 14 l/min which I think is pretty good from what I’ve seen online. The issue is the dynamic pressure which is only about 0.25 bar.

Can anyone help me understand how the flow rate can still be good with such a low dynamic pressure and what issues the low dynamic pressure might cause?

We’re renovating & going from cylinder boiler with pumped shower on ground floor to combi boiler & shower on first floor so concerned about potential pressure issues.

Also, I see from Ofwat & various water company websites that the regulatory minimum pressure is 0.7 bar although many companies voluntarily aim to provide 1.0 bar minimum, but is this static or dynamic pressure? I can’t seem to find any info on that.

Any info greatly appreciated!