Replacing main water lead pipe with MDPE.

4 Apr 2008
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United Kingdom
Hi all,

I moved into a house with no gas, my plan is to get the gas installed by SGN, at the same time I would like to take the opportunity of replacing the main water pipe made of lead with a MDPE pipe.

I have 2 questions:

1) I was advised to use a 25mm MDPE pipe, do stop cocks owned by the water supplier (in this case Scottish water) normally use 25mm compression fittings?

2) I am going to install a standard 25mm to 22mm compression stop cock but came across a MDPE stop cock. What is the advantage of using a MDPE stop cock knowing I will connect it to 22mm coper pipes?

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Unless you are more than 30 metres or so from the water main, 25mm will be fine. Deal with lead replacement used to be you get the new pipe to your property boundary and water board will do the rest for free (call them and check, when you put your pipe in leave enough on it to reach the water co's stoptap, they'll probably want to inspect the trench before you fill it as well). Water co will have connectors to mate your new pipe to the street tap whatever size it is.
MDPE to MDPE stop taps are cheaper than MDOE to 22mm. Also lets you have the stoptap (for example) in the garage and then continue to the house underground in MDPE (bury it direct) rather than 22mm (protection required). You'll need to drop to 22 eventually, whichever works best
Thanks a lot, very detailed answer and spot on! I called Scottish Water and they already sent me a form for a track inspection, they confirmed they will connect the MDPE pipe to the main stop cock for free.

Last question if I may, according to the regulations I believe that both the gas and water pipes need to be 350mm apart, however is it allowed for both the gas and water pipes to use the same entry point into the property? (meaning they would be less the 350mm apart)

I am asking because it is a 150 years old house with very thick stone walls, and listed, hence it would be pretty challenging to have to drill a new hole.
I don't know how your regs/listing conundrum would work out. Didn't know about the 350 separation either....give the gas board a call & ask for advice. They may be happy with ducting or other separation where clearance drops below that requirement
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Your water pipe needs to be laid at a depth of 750-1350mm below the surface; your gas pipe should be 375mm under the garden and 450mm under your drive.

Most gas meter installations are now buried boxes in the garden against an outside wall, so your gas service pipe would rise externally. Your water main will need to go in under/through your foundations then rise internally in an insulated duct. Gas and water pipes do not need to be 350mm apart inside your property

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