How much does a rainwater harvesting system cost?

Question

Our water bills keep creeping up and we've a big roof and garden so harvesting seems sensible. What does a proper underground tank system cost installed, compared to just sticking with water butts?

Ala · Answer

The cost of a rainwater harvesting system depends on the size of the property and the type of system required. As a rough guide:

Basic water butt system: £50–£300
Above-ground rainwater harvesting system: £500–£2,000
Underground domestic rainwater harvesting system: £2,500–£6,000+ (including installation)

The final cost depends on factors such as the tank size, excavation work, pipework, pumps, filters, and how many appliances (e.g. toilets, washing machines, or garden irrigation) will use the harvested water. A site survey is usually needed to provide an accurate quotation

Mark · Answer

prices start from £1500 depwnding on storage size and location

Charlie · Answer

A standard domestic rainwater harvesting system typically costs between £2,000 and £3,500 for the equipment alone, with total installation costs pushing the final price to anywhere between £3,000 and £5,000.

Ash · Answer

Overall the price of water butts would be a lot cheaper. 
You more use the rain water harvesting for your toilets etc and outdoor taps. Theres alot of work involved but if you’ve got the money to spend it’s worth it overall.

The last one I did was around £7000 all in but there will be different circumstances.

Benjamin · Answer

A proper underground rainwater harvesting system usually costs £3,000–£7,000 installed, whereas sticking with water butts is £40–£300 depending on size. The difference is massive — but so is the capability.
Here’s the breakdown so you can decide if the investment makes sense for your house.

1. Cost of a full underground rainwater harvesting system (UK, 2026)
✔ Basic domestic system (garden + outside taps only)
£3,000–£4,500 installed

Includes:
2,000–3,000 litre underground tank
Submersible pump
Filter and calming inlet
Basic control unit
Excavation + backfill
Pipework to garden taps
This is the most common setup for homes with large gardens.

Full domestic system (garden + toilets + washing machine)
£4,500–£7,000 installed
Includes everything above plus:
Header tank or direct‑feed control system
Plumbing into WC cisterns
Plumbing into washing machine feed
Automatic mains backup
complex filtration
Larger tank (3,000–6,000 litres)
This is the “proper” system people install when they want meaningful water‑bill reductions.

When it costs more
Deep excavation or poor access
High water table
Need for reinforced tank lid (driveway installation)
Very large roof area requiring bigger tank
Long pipe runs to the house
These can push costs to £7,000–£10,000, but that’s unusual for a terrace or semi.

3. Cost of water butts (the cheap option)
✔ Standard water butt (200–300L)
£40–£80

✔ Large decorative or slimline butts (300–500L)
£80–£150

✔ Multiple linked butts (600–1,000L total)
£150–£300

✔ Limitations
They overflow constantly in heavy rain

Water goes stagnant
Limited pressure (gravity only)
Not enough storage for a large garden
No integration with toilets or appliances
Manual filling, manual use
Water butts are cheap and cheerful — but they’re nowhere near a harvesting system in capability.

Gavin · Answer

you need to know the size of tank you will be using and the system what it is being used for (I'm guessing grey water for toilets)

Andrew · Answer

The cost of a rainwater harvesting system depends on its size and what you want to use the water for.
Typical costs in the UK are:
Basic water butt system (100–250 litres): £30–£150
Larger above-ground storage (500–2,000 litres): £300–£1,500
Underground tank for garden use: £2,000–£5,000 installed
Whole-house rainwater harvesting system (for toilets, washing machine, and garden): £4,000–£10,000+ installed, depending on tank size and the complexity of the plumbing.
For an average family home:
A 3,000–5,000 litre underground system typically costs £5,000–£8,000 installed.
If you're building a new home, installation is often cheaper because the excavation and plumbing are already part of the project.
If you're in the UK, rainwater harvesting can help reduce mains water use for:
Garden watering
Toilet flushing
Washing clothes
Car washing

How much does a rainwater harvesting system cost?

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