FYI mains water pressure

[scottishjohn]

I now am working on my planning  and one of things i noticed was the scottish water statement which says they only have to  supply you water at 1bar -

you could get more depending where you are --but  1 bar is minimum--so  I am guessing I will need to fit pump etc as my plots are up a hill--time will tell

something else to consider when buying a plot up a hill in countryside

 

 

[vivienz]

My plot is fairly rural and the water supply is a dribble on a good day so we are having an accumulator tank to overcome any supply problems in the house.

[Jeremy Harris]

It's the same in the rest of the UK, too. 

 

Be aware that you cannot (at least under water regs that apply here) fit a pump directly to a main that could lower the pressure to an excessive degree (specifically cause suction in that main that could suck in contamination through any leakage in their system), either.  If you fit a pump there is often a requirement for a break tank that's filled by the low pressure main, then a booster set and accumulator can draw from that to feed the house.  If a break tank is fitted then it is very sensible to also include water disinfection, as the sealed supply will have been opened to air, residual disinfection provided by the water supplier will be lost, and airborne contamination is a real risk (same risk as having a cold tank in a house and not using it for drinking water).

 

There are booster pump and accumulator sets available that include supply-side pressure monitoring, I believe.  I've not used them, but they may be a solution that satisfies the water regs and also avoids the need for consumer-side disinfection.

 

Before you do anything, though, I would get a peak reading pressure meter and fit it to the supply where it comes in, via a non-return valve, as that's a cheap and easy way to tell you what you really have at the incoming supply.  If you get a peak reading that's well over 1 bar (and I strongly suspect you may, as pressure increases a lot at some times of the day or night) then an accumulator will fix your problem with no requirement for a pump or further disinfection.  I'm really impressed with the pressure and flow stability we get from our accumulator, it really does make a big difference, not least of which is in reducing interaction between outlets (so no problems with shower fluctuation when a toilet is flushed or the washing machine turns on).

[ProDave]

Wait until you get the supply (arrange it's connection sooner rather than later) then you will know. 

[lizzie]

I did a lot of research into the accumulator tank set up as we could not get water connected to test pressure and I was led to believe it may be low.  We provisioned for an accumulator in the garage.  In the event we did not need the accumulator as pressure was ok but I still have the main coming up in the garage and going back out to the house - its just an above ground insulated loop.  If ever pressure did drop I can fit an accumulator system.  They are not cheap.  The ones I was looking at use UV as the disinfectant.

[Jeremy Harris]

2 minutes ago, lizzie said:

They are not cheap.  The ones I was looking at use UV as the disinfectant.

 

They vary a fair bit in price, and you need to shop around.  We have two 300 litre accumulators in parallel (for space reasons) and IIIRC they were around £300 each.  One would probably be enough, I only fitted two as we have a high flow filter backwash requirement, which is unique to our setup.

 

There's no requirement for UV disinfection with just an accumulator and NRV fitted in the line, as the system remains closed and sealed.  There's only a need for additional disinfection if there is a break tank and pump, due to the possibility of contamination entering the open break tank.

[lizzie]

We would have needed to pump from garage to house and as it included our drinking water then we were advised that disinfectant was necessary.  I forget the regulation but I was given it at the time.

 

i think it depends on if you pump, if you need an accumulator then it is a possibility you will need a pump to get any decent pressure for showers (so I am told) but I am single storey and have no cold water tanks in the house my cold water is all direct mains so no doubt that makes a difference.  

[Jeremy Harris]

There's no need for additional disinfection as long as the water supply isn't opened up to air or contamination.  Pumps are sealed units, so contamination can't get in, as are accumulators.  There's nothing in the water regs that recommends or requires secondary disinfection for a mains water supply that remains sealed from the water main to the point of use in the house, as the residual disinfection that the water companies use will remain effective.

 

The issue only arises usually when a break tank is fitted, or if some form of water treatment that involves aeration is used, and for both of those cases secondary disinfection is a good idea. 

 

Much of the time low pressure from the supply can be resolved just by fitting an accumulator, after the mandatory double non return valve from the main, as low pressure is often just a transient, demand related, event, that an accumulator can get around.

 

Pumps sets directly connected to a mains water supply to charge an accumulator create a host of issues, the primary one being that if directly connected (so avoiding the need for secondary disinfection) they must have a way of preventing the incoming mains pressure dropping below a set level, and must definitely have a device that turns the pump system off if there is suction on the mains input side.  The water companies quite rightly get upset at the pressure being dropped to the point where contamination can get sucked into their network.

[Ed Davies]

But normally you'd put the pump, if one's needed, after the accumulator, wouldn't you? If so, would you have to have something to stop the pump running when the accumulator is empty, to prevent sucking the mains input then?

[Jeremy Harris]

12 minutes ago, Ed Davies said:

But normally you'd put the pump, if one's needed, after the accumulator, wouldn't you? If so, would you have to have something to stop the pump running when the accumulator is empty, to prevent sucking the mains input then?

 

 

No, the pump is there to get the accumulator up to pressure, and is turned on and off with a pressure switch on the output side that will typically have around 1 bar of hysteresis.   Typical settings would be to have the pump turn on when the accumulator drops to about 2.5 bar and off when the accumulator reaches about 3.5 bar.  These are the settings we use and in practice you can't notice the 1 bar drop before the pump kicks in.

 

The idea is to make sure the pump only operates when needed, and to let the accumulator do the task of maintaining a fairly steady supply pressure to the outlets.  This also means that the pump doesn't have to be sized for the short duration, peak demand, as the accumulator will have enough reserve to meet that, and can deliver a flow rate that is probably an order of magnitude greater than that of the pump for short periods.

[epsilonGreedy]

My concern is too much water pressure, full whack from the builder's standpipe hurts my hand and I am worried it might blow the fittings of my onsite static caravan.

 

How can I assess my water pressure beyond a timed bucket fill test at the standpipe? The incoming pipe is 25mm.

[Mr Punter]

Just now, epsilonGreedy said:

My concern is too much water pressure, full whack from the builder's standpipe hurts my hand and I am worried it might blow the fittings of my onsite static caravan.

 

How can I assess my water pressure beyond a timed bucket fill test at the standpipe? The incoming pipe is 25mm.

 

The bucket fill does not test static pressure, just flow rate.  If you want lower pressure, fit a pressure reducing valve.

[Jeremy Harris]

Just now, epsilonGreedy said:

My concern is too much water pressure, full whack from the builder's standpipe hurts my hand and I am worried it might blow the fittings of my onsite static caravan.

 

How can I assess my water pressure beyond a timed bucket fill test at the standpipe? The incoming pipe is 25mm.

 

Timing flow into a bucket can't measure pressure, only flow rate.  To measure pressure then fit a pressure gauge, ideally with a non-return valve in series, as that will then capture the peak pressure available (there will often be a significant difference between the minimum and maximum pressure available at the main supply).

 

It's not uncommon to get a pressure as high as 5 or 6 bar on a water supply, so I'd suggest getting a 10 bar gauge.

[PeterW]

@epsilonGreedy sounds like you have 4-5 bar which will need dropping for both the van and the house.

 

I've got a spare PRV that will take it down to 3 bar but you would need to wrap it well in insulation if its not inside the van over winter.

[epsilonGreedy]

1 minute ago, JSHarris said:

It's not uncommon to get a pressure as high as 5 or 6 bar on a water supply, so I'd suggest getting a 10 bar gauge.

 

 

I suspect I will see a high number for both static and dynamic pressure as I have never experienced such a phenomenal water supply. This is a good thing long term though just a bit of a challenge I suspect for an aging static caravan that has previous frozen water damage and with garden hose fittings that blow off.

 

A quick look at Screwfix shows such pressure gauges selling at between £15 and £34.

[epsilonGreedy]

25 minutes ago, PeterW said:

I've got a spare PRV that will take it down to 3 bar but you would need to wrap it well in insulation if its not inside the van over winter.

 

 

Thank you for the offer, I assume such a valve cannot be located underground? The Gassafe fitter might insist on a prv next week when he visits to commission the van's central heating. I will get back to you.

[PeterW]

It can’t go underground and will have 22mm in and out so probably best as soon as you come into the van. 10 mins to fit as it’s a reducer and you could just vent back to the ground below 

[lizzie]

Ive just checked back and it was installer who said it should be disinfected as best practice not regulation.  The pump goes after the tank from his spec. 

 

Before the water was in local water co advised me to expect 1.5bar..a dribble...the water board man recommended a tank and pump system to ensure good pressure and showers etc.

 

As they took 18 months to get the water in and we had pretty much built a house by then we had to provide for this solution but given the costs I was quoted we elected to do the provision only not buy tanks and pumps etc until water in and and we saw what we ended up with.  I’m very glad we did that because although it cost us a little more on the groundworks end we saved a fortune on tanks etc because when water finally came in it was at 5 bar.  I have constant readings of between 5 and 6 bar on my system now .......great showers nice and powerful even with a 30cm shower head. Think they put pressure reducers on the basin taps.  Whatever they did I have a great water supply throughout the house and no cold tanks or pumps.

[joe90]

I think the 1 bar is worst case senario, we were told water pressure out here in the sticks was not good and we get 6 bar !!!!

[Jeremy Harris]

1 hour ago, lizzie said:

Ive just checked back and it was installer who said it should be disinfected as best practice not regulation.  The pump goes after the tank from his spec. 

 

Before the water was in local water co advised me to expect 1.5bar..a dribble...the water board man recommended a tank and pump system to ensure good pressure and showers etc.

 

As they took 18 months to get the water in and we had pretty much built a house by then we had to provide for this solution but given the costs I was quoted we elected to do the provision only not buy tanks and pumps etc until water in and and we saw what we ended up with.  I’m very glad we did that because although it cost us a little more on the groundworks end we saved a fortune on tanks etc because when water finally came in it was at 5 bar.  I have constant readings of between 5 and 6 bar on my system now .......great showers nice and powerful even with a 30cm shower head. Think they put pressure reducers on the basin taps.  Whatever they did I have a great water supply throughout the house and no cold tanks or pumps.

 

Pump after tank as a configuration means the tank must be a break tank, that allows air ingress, and that's why you needed secondary disinfection.  The accumulator would have been on the output side of the pump (has to be one there - the pump won't work properly without one, as water is (to all intents and purposes) incompressible).

 

The scenario for using a pump to reinforce mains water pressure is to have a break tank filled by the mains supply via a float valve, the pump draws from the break tank and fills the accumulator (with a pressure switch to turn the pump on and off based on the accumulator pressure) and then a UV disinfection unit at the feed point to the house.

 

If you have variable pressure, and just need an accumulator to even it out and give a robust supply, the the set up is different.  The incoming mains supply feeds the accumulator directly, via the normal double non-return valve that has to be fitted to the incoming supply, and the feed to the house comes from the accumulator directly.  No secondary disinfection is needed as the system remains closed.

 

The first step in finding out what might be best is to monitor the peak pressure on the incoming supply, ideally at several different times during the day, so that you can find out how stable the pressure is and whether there is a long enough period at an adequate pressure to charge the accumulator.  The size of the accumulator is set by the demand during low mains pressure time periods, bearing in mind that the useful water volume in an accumulator is less than half the stated volume, because of the air volume on the outside of the bladder.

[Temp]

11 hours ago, scottishjohn said:

I now am working on my planning  and one of things i noticed was the scottish water statement which says they only have to  supply you water at 1bar -

you could get more depending where you are --but  1 bar is minimum

 

Just to echo what others have said..

 

That's the legal minimum they are obliged to provide, same in England. However in practice it's very site specific. In many places you actually get >3 bar.

 

Before deciding on anything you should measure the actual static pressure on site and the flow rate you get from an open pipe in liters per min. You may not need to do anything, no pumps or storage tanks.

Edited November 27, 2018 by Temp