Trench for water connection and waste pipe

[Ralfbean]

Hi all, 

 

Just wanted clarification on whether it is possible to have waste pipe and water pipe in the same trench? I have a narrow lane down to the water and sewer connections on the road and ideally would like to lay in the same trench.

 

How does this work and can I lay together?

 

Any advice would be great!

 

Thanks!

[MikeGrahamT21]

Personally I can't see a problem with this, as long as the water pipe is properly insulated as it should be in any trench, and pea gravel I think this should be fine.

[Ralfbean]

Thanks Mike, appreciate the response

[Russell griffiths]

I would, but I would do it a bit differently. 

Wider trench so water one side drains on the other, the reason being your drain has to run at a certain angle to get the flow so you will need to do some careful calculations to get the depth of the trench correct, the water company will also want the water pipe at a specific depth, so yes but will require a bit of thought. 

[Mr Punter]

No issue.  Depending on invert levels for the drains you can lay the water in the bottom and the drain over this if you want.  What about BT, gas and electric?  If you are doing all you need to plan quite carefully.  The water company often need to inspect the trench to make sure it is at least correct depth - often 750mm.  If there is a driveway above and you are having deliveries make sure all the services are well buried and the trenches are properly compacted with decent fill material, or they will get trashed.

[ToughButterCup]

It might be a bit easier than our local tame Overthinker (above @Russell griffiths) thinks ...

The water company will give you a specification to which you have to lay your pipe.  That's a given. (600mm locally)

You will also have an invert level for the foul drain outflow from your house, and a target invert level for the sewer (or treatment plant) to which you want to connect. 

Assuming (at a guess) you want a 1 in 60  or a 1 in 80 slope (17mm or 12.5mm per meter respectively) then it should be reasonably easy to calculate whether the two services will bump into one another vertically.

 

In our case the invert for the foul drain was always much deeper than 600mm (at least 1330mm below ground level).  So, if we had to put both services in one trench, then we could always have separated both services by at least 500mm vertically.

 

Dont forget the warning tape.....? ... like I did. 

[Conor]

Ok, from my point of view from the water industry. We'd always avoid doing this. And you'd never have the water pipe in the same bedding material as the sewer, especially below. The scenario is that a leak in the waste system could enter the water pipe if it were at the same level or lower and in the same bedding material as the waste pipe. (This scenario can easily happen if you have a leaking pipe and low pressure or no water event, when the hydrostatic pressure in the ground is greater than in the pipe) This has happened in public water supplies and lead to serious health incidents.

 

You will need to bury your water pipe at about 900mm deep. See what the invert requirements are for your waste and take it from there. If the water pipe is more than 400mm (100mm bedding for each service separated with clay) deeper than than the required depth for the water pipe, you'll be fine.

[ToughButterCup]

2 hours ago, Conor said:

Ok, from my point of view from the water industry. We'd always avoid doing this. And you'd never have the water pipe in the same bedding material as the sewer, .... If the water pipe is more than 400mm (100mm bedding for each service separated with clay) deeper than than the required depth for the water pipe, you'll be fine.

 

Thanks very much. An extremely useful post.

Ian