The cold water supply to kitchen sinks and bathroom washbasins

[@TonyC]

For residential housing, what are the current regulations and/or recommended/standard practices regarding the supply of cold water to the taps on kitchen sinks and bathroom washbasins? Must the supply come directly from the mains or can it come from the cold water storage tank? Or is the situation more complex than this?

In case it is relevant, I will explain the stimulus for this query. I’ve always lived in a house where the cold water supply to the kitchen sink and bathroom washbasins has come directly from the mains. And this is the situation in our current house which was built in 1979.

My wife and I are now considering moving to a house that was built in 1988. However, the current owner of the house believes that only the cold water supply to the kitchen sink comes directly from the mains, and the cold water supply to the washbasins in the two bathrooms comes from the cold water storage tank. Frankly, I don’t relish the thought of cleaning my teeth and rinsing my mouth with water that has come from the cold water storage tank, let alone drinking a glass of cold water from a tap on one of the washbasins if I feel thirsty in the middle of the night.

I know that it is relatively easy to test where the supply of cold water comes from for each of the taps. But suppose the situation is as the current owner believes. As a general rule, how easy or difficult would it be for a plumber to change the pipe layout so that the cold water supply to the taps on the bathroom washbasins comes directly from the mains? (I appreciate that this might be a “how long is a piece of string” type question but I thought I would ask it anyway!)

 

[fowlerboi]

That used to be standard practice. Mains for the kitchen sink and the storage tank does the rest of the house. I fully expect at some point you lived in a house which had that exact system. There are also millions of people in the UK that still have that system

A plumber would need to test the mains pressure and flow rates before making a recommendation on which system you could go with but the options are:

Back feeding the colds from the mains- this will depend on pipe layouts and if you're happy taking carpets up in a number of rooms

Install a combi boiler- this will mains pressure the hots and colds and can do so with minimal disruption but the cost is higher to install

Install an unvented cylinder- This will allow stored mains pressure hot water, this system vs a combi will be for your plumber to discuss with you and will depend on various factors about water usage

 

[@TonyC]

... but the options are:

Back feeding the colds from the mains- this will depend on pipe layouts and if you're happy taking carpets up in a number of rooms

Install a combi boiler- this will mains pressure the hots and colds and can do so with minimal disruption but the cost is higher to install

Install an unvented cylinder- This will allow stored mains pressure hot water, this system vs a combi will be for your plumber to discuss with you and will depend on various factors about water usage

Thank you for the reply.

Yes, the conventional boiler in the house we are considering moving to is 14 years old, so it is probably near the time to replace it. I was actually thinking of installing a new system boiler and hot water cylinder, which require neither a cold water storage tank nor an expansion tank in the loft.

Instead of having to lift carpets, floorboards, etc., would it not be possible simply to intercept the mains water supply to the cold water storage tank in the loft and divert the supply to the output pipe from the cold water storage tank, effectively bypassing the tank altogether? Or is that too simplistic a solution? I can envisage one possible problem of doing this if taps, showers, pumps, etc. further down the pipework were not designed for mains pressure water. Or am I wrong in thinking that it might be a problem?

 

[fowlerboi]

Exactly that. Certain fixtures won't work if the cold is mains and the hot is gravity fed.

 

[@TonyC]

Exactly that. Certain fixtures won't work if the cold is mains and the hot is gravity fed.

Thanks again. But actually, the scenario I was thinking of was a combination of bypassing the cold water storage tank, as described previously, and replacing the existing conventional boiler with a system boiler and its associated hot water cylinder. Wouldn't the hot water from the cylinder then be under same mains pressure as the cold water?

 

[fowlerboi]

Sorry. I was replying to the question about bypassing the storage tank.

What you propose is an unvented cylinder outlined in my first reply

 

[Ben-gee]

Yes potentially your existing pipework could have connections that are watertight under gravity conditions but may not be so once pressurised to mains pressure.

You either reuse existing pipework aware that leaks may appear - of run new pipework.

Depending on how accessible existing pipework is it should be fairly easy to rectify any problems that crop up, however if buried in walls and concrete floors that will not be the case.