Off-Grid · Water · Rainwater
Rainwater: The Obvious First System to Build
A roof, some gutters and a tank catch far more water than you'd think — and it's cheap, simple, and the first system worth building on any off-grid plot. It won't be your drinking supply without treatment, but for the garden, the loo and the washing it's free water falling on a roof you already own.
Rainwater is the workhorse of an off-grid water setup: it takes the pressure off whatever your drinking source is, it's legal and easy for most household jobs, and you can build it in stages as the budget allows.
In France, harvested rainwater is fine and legal for the garden, flushing the loo and outdoor jobs — and washing, if you plumb it right. What it is not, untreated, is drinking water. Keep that line clear and rainwater does most of the heavy lifting while a smaller, cleaner source handles the tap.
All four routes to water compared over 5, 10 and 20 years.
Read the hub →🚰 An existing well or springCheaper still if the plot has one — the jackpot to check for before you lean on rainwater alone.
Read the guide →🕳️ Drilling a boreholeThe big-money route — and why to think hard before you pay to drill.
Read the guide →How much can you actually catch? more than you think
A roof is a big catchment
Even a modest roof turns a rainy French winter into thousands of litres. Rainfall in the central and western belts is generous for much of the year, so catchment is rarely the limit — storage is. The question isn't "will it rain enough" but "have I got the tank to hold the winter's water through a dry summer."
Storage is the real design choice
A couple of IBC totes get you started cheaply; a buried cistern holds a proper reserve and keeps the water cool and dark. Size the store to bridge your driest stretch — the more you can hold from the wet months, the further rainwater carries you into a dry August.
The kit, in order
Gutters → first-flush → tank → pump
Collect off the roof into good gutters; a first-flush diverter throws away the dirty first run that carries roof muck; the clean water goes to the tank through a leaf filter; a pump (off your solar) pressurises it to the house. It's simple, cheap plumbing anyone handy can build and extend.
Keep it dark and covered
Light grows algae and open tanks grow mosquitoes. Covered, opaque storage keeps rainwater clean and usable for far longer — a small detail that makes a big difference to water quality.
Drinking from it — only with treatment
Roofs are dirty; treat before you drink
Rain is clean; the roof it runs off isn't — bird mess, dust, moss. For non-drinking uses that's fine. To drink rainwater you run it through a proper filter-and-UV treatment train and test it, exactly as you would a well. Many off-grid homes simply keep rainwater for everything except the tap and lean on a cleaner source for drinking — a well, or a borehole if the ground forces it — which is the simplest, safest split.
What it costs
DIY ranges — scales with how much storage you build. See how it stacks up against the other routes in the cost table on the water hub.
- £150–500A starter setup — gutters, first-flush, a couple of IBC tanks and a small pump. Garden and loo sorted.
- £800–2kA proper system — a buried cistern for real reserve, good filtration, a pressure pump plumbed to the house.
- £150–400A treatment train on top, only if you intend to drink it rather than keep a separate drinking source.
Rainwater plus a clean source is the sweet spot
Rain for the garden and loo, a well or treated supply for the tap. See where it fits in the whole off-grid build — power, water, waste and warmth.
See the whole off-grid plan →