Water in the Ground in Orpington: Leak or Groundwater?

Do a meter test before you do anything else. Turn off every tap and appliance, read the meter, and read it again 30 to 60 minutes later without using any water. If the numbers have moved, you have a leak on your side and it needs finding. If they have not, and the wet ground appeared after weeks of rain and your neighbours have it too, you are most likely looking at groundwater, which is a drainage and flood matter rather than a plumbing one.

Why Orpington gets both

Orpington sits on the line where the chalk of the North Downs meets the clay. You can see that line at Priory Gardens, where the River Cray rises from a spring-fed pond: water that has soaked into the chalk comes back out where it meets the clay. In a long wet winter the water table in the chalk rises, and it can come up in gardens, cellars and low roads that are dry the rest of the year.

This is not theoretical. Bromley Council’s flood risk assessment records groundwater flooding in Orpington in the winter of 2014, on highways and in gardens, and surface-water flooding at Borkwood Court in February 2014. The same assessment lists winter 2014 groundwater in West Wickham, Biggin Hill and St Mary Cray, including below-ground car parks. A neighbouring-boroughs groundwater group was set up after that winter for exactly this reason.

At the same time, Orpington’s clay side moves. It shrinks in a dry summer and swells in a wet one, and old supply pipes under the front gardens of the 1930s semis in Crofton and the post-war houses at Ramsden, Goddington and Green Street Green crack as it does. So a wet patch in an Orpington garden really could be either.

How do I do the meter test?

1. Find your water meter, usually in a small chamber under a lid in the front path or pavement, and lift the lid.
2. Turn off every tap, the washing machine, the dishwasher, and make sure no toilet is refilling.
3. Write down the full meter reading, or take a clear photo of it.
4. Wait 30 to 60 minutes without using any water at all.
5. Read the meter again and compare.
6. If it has moved, turn off your internal stopcock and watch the meter for another ten minutes to see which side of the stopcock the leak is on.

If the meter keeps moving with your stopcock off, the leak is on the underground pipe between the meter and the house. If it stops, the leak is indoors: a toilet cistern passing water into the pan, a pipe under a floor, or a loft tank overflowing.

What else points to groundwater?

• It came after a long wet spell, not overnight in dry weather.
• The water is clear and cold, and it seeps rather than gushes.
• Your neighbours have it too, or the road has standing water in the same low spot.
• It rises and falls with the weather over days and weeks.
• The meter is still when everything is off.

What points to a leak?

• The meter moves with every tap off.
• The wet patch is in a line, often between the outside stop tap and the front wall.
• It stays wet in dry weather, or there is a green strip in an otherwise brown lawn in August.
• Your pressure has dropped, or your water bill has jumped.
• Only your property is affected.

The leak is mine. What now?

Thames Water supplies Orpington, and it is clear that the supply pipe under your garden and driveway is yours. Once you know there is a leak on your side, Thames says you must fix it within four weeks. If you are on a meter and get it fixed in that time, you may be able to claim a leak allowance for the water lost.

The best way to do this is to locate the leak precisely before anyone digs. Acoustic listening, ground microphones and tracer gas can usually pin a supply leak to a small area, so you get one hole in the lawn rather than a trench. If the old pipe is lead or galvanised iron, replacing the whole run with new plastic pipe is often the sensible repair. Our leak detection in Orpington page explains how it is done.

It is groundwater. What now?

A plumber cannot fix groundwater. What you can do:

• Check your address on the Environment Agency’s long-term flood risk service on gov.uk, which covers groundwater as well as rivers.
• Sign up for free flood warnings on gov.uk.
• Report flooding of roads and public land to Bromley Council, which is the Lead Local Flood Authority for the borough.
• If water is getting into a cellar or under a floor, talk to a damp-proofing or drainage specialist about tanking or a sump pump.

Our guide to a wet cellar in Sydenham deals with the same question on a steep clay hill rather than a chalk valley, and the meter test is the same.

What if I am not sure?

If the meter moves even slightly, treat it as a leak until it is ruled out. A slow leak and a wet winter can happen at the same time, and groundwater does not make your meter turn. More about the area on our Orpington page.

Need a plumber now?

If your meter is moving, or water is coming into the house, Call 07868 281022. Tell us your postcode, where the water is showing, what the meter is doing, and whether the stopcock is off. We cover water leaks in Orpington across BR6 and we agree the price with you before any work starts.