Standing water in basement. Sump pump? *PigletJohn*

[Caitmous]

Under the communal hall of our converted London victorian house is a five foot 'basement' (crawl space?) that has a foot of clear, fresh smelling groundwater in it all year round.

Because it is under a carpet in a communal area it's never been spotted in surveys etc.

We have had a quote by a damp proofing company for £13k to have a sump pump fitted.

Is this the best remedy?

I have read both a) that it is common and not a problem and could be left alone and that b) pumping can cause additional harm by removing soil from the foundations.

We are a self-managing block so there is no management company to sort this.

Any advice?

I would certainly start by trying to find the source of the water. First thing, get the water co to test it. They can detect tapwater from a watermain because it is chlorinated. They can also recognise gutter water because it has leaf fragments, and sewer water because it has soap. Victorian water pipes are very likely to be leaking by now, as are old drains. As you are a block I don't suppose you have a meter under the pavement, which would be useful for detecting leaks.

A leak may also be in your neighbour's pipes.

If it is truly groundwater (perhaps you live in a dip?) dig a deep hole in the garden and see if it fills up. All your neighbour's cellars would have water at the same height.

A London house will be built on clay, so pumping out will also pump that away as fine mud. Sumps should be lined with porous concrete which allows water to pass but not mud, but clay particles are very fine so if you go down this route take advice from a specialist contractor with a good track record.

Regardless of remedial action, you need the void to be very well ventilated with a lot of air bricks all round the building that are not clogged with cobwebs and dust. It is bound to be damp and humid. There is a considerable risk of rot, though strong ventilation will keep it cold by evaporation.

My dads rental property had this problem, also in London. Apparently a spring had sprung up I think he has a pump and lots of air bricks...