Off-Grid · Water · Borehole
A Borehole: The Expensive Gamble to Get Right
Drilling your own borehole (forage) sounds like the ultimate off-grid move. It's also the fastest way to pour thousands into the ground and still need hundreds more in checks — and to end up with a hole that's dry, weak, or full of water you can't drink. This is the page that saves you money by talking you out of rushing it.
A borehole is the last resort on the water table, not the dream. Sometimes it's the right answer — a remote plot, no well, no nearby main, not enough roof for rainwater. But it's the one option where rushing in costs you the most, so the homework comes first.
The drill is sunk cost whether or not you hit good water. You pay the driller for the hole, not for a result. So the money that matters isn't the £5,000–10,000 to drill — it's the few hundred you spend beforehand finding out whether there's worth drilling for. Skip that and you're gambling thousands on a hunch.
Check for this first — often already on the plot, and always cheaper than drilling.
Read the guide →🌧️ Rainwater harvestingCheap and simple if there's roof to catch it — worth costing before you ring a driller.
Read the guide →🧪 Making it drinkableWhat deep water often needs before it's safe to drink — factor this into the sum.
Read the guide →The homework that comes first hundreds, not thousands
Ask the neighbours and the mairie
The cheapest research is free: neighbours with boreholes know the local depth, yield and water quality better than any brochure. The mairie and local drillers know the area's groundwater. A morning of asking around tells you most of what a speculative drill would cost thousands to discover.
Check the groundwater data
France keeps national geology and groundwater records (the BRGM's data, via InfoTerre) — depth to water, aquifer type, existing declared boreholes nearby. It's the same "read the ground before you commit" discipline as the clay check, and it's largely free. A hydrogeologist's siting opinion costs a few hundred and can save you the whole drill.
Then budget the checks the drill still needs
Even after a successful drill you're not done: a flow/yield test to prove it gives enough, a potability test (£100–300), and a déclaration en mairie — every domestic borehole must be declared. These hundreds are part of the real cost, not an afterthought.
What can go wrong and often does
Dry, or too weak to bother
You can drill to full depth and get a trickle — or nothing. The driller still gets paid. A low-yield hole that can't refill fast enough for a household is money spent for a garden tap.
Water you can't drink without a fight
Deep water can carry iron, manganese, sulphur, nitrates or bacteria. Then you're buying a serious treatment setup on top of the drill — more cost, more upkeep. The hole was only ever half the job.
The honest comparison: a borehole vs the mains do this sum
A mains connection is often cheaper — and carries no risk
Before you romanticise drilling, get a written mains-connection quote, the way you'd get an Enedis quote for electricity. If a main is anywhere near the plot, a connection plus twenty years of a frugal one-person water bill frequently comes in well under the all-in cost of a borehole — and there's no chance of a dry hole. On the cost table, a new borehole is the dearest option at every horizon. Off-grid should be a choice, not an expensive accident.
When a borehole does win
Remote plot, no usable well, no main within reach, not enough roof or storage for rainwater — and good local evidence of water at a sensible depth. There, a properly-sited borehole is a genuine, permanent asset. The difference between a triumph and a money-pit is entirely the homework you did first.
What it really costs
All-in ranges. The drill is the big number; the checks and treatment are the ones people forget.
- £5–10kThe drilling itself — deeply depth-dependent, and paid whether or not the water's good.
- + £1kPump, rising main and install once you've hit usable water.
- + £100sSiting advice, flow test, potability test, and the declaration — the "hundreds on top" that are not optional.
- + maybe £100sTreatment, if the water needs it — and deep water often does.
Water is one system of four
However you get water, it's only part of going off-grid — power, waste and a warm room complete it. See the whole build in order.
The whole off-grid build →