Water supply sizing query

[Annker]

I'm at the beginning of a big renovation project. One of my first tasks is to prepare a carpark for the arrival of tradesmen so I'm getting affected buried services upgraded now, save reopening ground down the line.

 

Existing water supply pipe is 1" lead which I am going to replace with MDPE.

South East Water have confirmed I can work on customers side of the meter and even better once the job is complete I can send on the associated invoices incurred, to which they will credit back to my SE Water account to the value of £250. I think that's reasonable offer myself!  

 

I have excavated customer side of the meter box chamber and it appears that the supply from the meter is 20mm MDPE which is then compression fitted on to the 1" lead.

As in the photo below its not obvious how the MDPE supply connects to the meter as it appears that the 20mm MDPE pass by the box chamber and out towards the road. All I can think is that the MDPE loops back on itself and connects to the underside of the meter. I'm not sure if that arrangement is possible, it seems torturous but seemingly it must take that kind of route.

Just to note that the meter is not bypassed; flush the toilet and the meter records it.

 

Is 20mm MDPE supply from the meter sufficient for a large 4 bed property (4 ensuites, downstair loo, and all the other standard requirements)? 

Before I had unearthed the 20mm I had it in my head that I would replace the 1" lead with 32mm MDPE, however if the supply immediately exiting the meter is only 20mm surely that will limit the flow gains a 32mm diameter pipe would offer?

I also note that the mains stopcock in the meter box chamber doesn't completely shut off the supply. I wonder if I could raised that as an issue with SE water and then perhaps they would kindly replace the stopcock and as the path is open allow me to remove the couple of foot of 20mm allowing me to connect a new 32mm MDPE to the meter?  

 

 

  

[saveasteading]

Now, I am not expert but will say something then others can chip in.

 

I think 25mm is standard. But if the water pressure is consistently high then 20mm may be enough.

 

Unless the water company changes that short piece, there will be a throttle effect there even if you put a bigger pipe in.

 

Is there enough water in the house now?

 

If nothing in the house is running then there must be a leak in either the lead, or mdpe or at your side of the meter.

 

Once you have taken the lead connection off, i would fit a valve, then you can turn it off and see if the flow has stopped, before connecting the new pipe.

Do you leave that valve on the system for your convenience in emergency or is it an unnecessary additional leak point?

[TonyT]

Flow cup and measure the flow?

[Annker]

@saveasteadingI am not sure if you or I understand the other correctly, I don't believe there is a leak currently.

 I have only just bought the house so I'm not entirely sure if the current flow/pressure is sufficient other than it isn't particularly strong; however given the current plumbing systems age, likely its not configured efficiently and therefore producing low pressure at the tap.

 

@TonyTYeah, I will do this. I have a pressure gauge attachment so those too metrics would be useful. I will have to do a bit of rooting to find a outlet directly on the main pressure to get a correct reading.

[saveasteading]

4 hours ago, Annker said:

mains stopcock in the meter box chamber doesn't completely shut off the supply

Sorry, I have read it properly now.  You can't turn it off, rather than it's running all the time.

 

Yes they should fix that for you. 

[saveasteading]

1 hour ago, saveasteading said:

Yes they should fix that for you. 

in fact they must fix it or you will have water pouring out when you remove the lead pipe.

[Annker]

1 minute ago, saveasteading said:

in fact they must fix it or you will have water pouring out when you remove the lead pipe.

Yes correct.

When I twist the stopcock key fully down there is still water running from the tap, similarly when I flush the toilet I can see the meter running which also indicates the stopcock is not fully shutdown. I believe this could be that the gate in the stopcock doesn't fully shut.

 

It is probably not enough of a flow to completely prevent me making on the new MDPE connection, but as you well know these "5 minute jobs" always take an hour and then by that time I'm up to my elbows in water🤿 

[jayc89]

11 minutes ago, Annker said:

Yes correct.

When I twist the stopcock key fully down there is still water running from the tap, similarly when I flush the toilet I can see the meter running which also indicates the stopcock is not fully shutdown. I believe this could be that the gate in the stopcock doesn't fully shut.

 

It is probably not enough of a flow to completely prevent me making on the new MDPE connection, but as you well know these "5 minute jobs" always take an hour and then by that time I'm up to my elbows in water🤿 

 

We had similar when re-routing a cold supply when laying a new slab. No internal stop cock, external one didn't shut off fully. Plumber had me blowing down the end of a copper pipe whilst he soldered the joint. Proper Laurel and Hardy moment.