Even England, the driest of the UK nations, averaged roughly 870 mm of rain a year over 1991–2020, more than enough for a well-designed rainwater harvesting system to make a meaningful dent in household water consumption.1 In the 2025 drought, hosepipe bans covered nearly 9 million people in England.2 With water bills rising too, harvesting the water that falls on your roof is increasingly practical rather than merely eco-friendly.

A rainwater harvesting system captures water from your roof gutters, filters it and stores it in a tank (above or below ground). It then supplies that water to non-potable uses: toilet flushing, washing machine, garden irrigation and external taps. In Environment Agency case studies, systems serving those uses cut mains water consumption by 40–50% compared with homes without one.3

System Types

Simple Water Butts

The entry point costs about £60–£90 for a 100–230 litre water butt kit with a downpipe diverter and stand. No installation skills required. Only practical for garden watering, too small and too low-pressure to supply toilets or a washing machine. A family with a 75 m² garden will exhaust a single butt in a couple of dry weeks.

Above-Ground Tank Systems

Tanks of 1,000–5,000 litres can be housed in a garage, outhouse or external compound. A pump draws water to the point of use. Suitable for garden irrigation and external taps; can supply toilets if the pump pressure is adequate. Easier to install and maintain than underground systems but visually prominent.

Underground Tank Systems

The most capable and discreet option. A reinforced polyethylene or concrete tank (typically 1,500–10,000 litres) is buried in the garden. A pump and controller switch automatically between harvested water and a mains back-up when the tank runs low. Supplies toilets, washing machine and garden. Requires excavation and connection to the building’s cold water feed.

Cost Breakdown

System TypeSupply OnlyInstalled Cost
Water butt kit (100–230 L)£60–£90£60–£90 (DIY)
Above-ground tank (1,000 L)£300–£600£600–£1,200
Underground system (2,500 L, garden use only)£800–£1,500£1,800–£3,000
Full underground system (2,500 L, toilet + laundry + garden)£1,500–£3,000£3,000–£5,500
Retro-fit to existing building (extra pipework)-add £500–£1,500

Costs assume average UK labour rates and a single-family detached house. Clay soil, high groundwater or difficult access can add £500–£2,000 to excavation.

Savings Potential

The average person uses around 140 litres of water a day.4 Toilet flushing and the washing machine are the main indoor uses harvested water can take over, and garden watering adds further demand in summer. Thames Water’s metered charges from 1 April 2026 are £2.7346 per m³ for clean water and £1.4721 per m³ for wastewater.5 A family of four saving 50 m³/year in mains water would save about £137/year on the clean-water charge alone, and up to about £210/year where the wastewater charge falls with it.

That gives a raw payback of roughly 15–40 years on a £3,000–£5,500 system, before pump electricity and maintenance, which is too long to make purely financial sense for most homes. The value proposition improves significantly if you:

  • Have a swimming pool, hot tub or large garden requiring substantial irrigation
  • Run a washing machine very frequently (five or more loads per week)
  • Are in a high-tariff water area or on a private supply with high treatment costs
  • Can incorporate the tank during a new build or major extension (reducing excavation costs)

Planning Permission

In England, a water butt or a buried rainwater tank at a house does not normally need planning permission, and a larger above-ground tank is best kept within the permitted development limits for garden buildings and enclosures under Class E, which rule out anything forward of the principal elevation of the house.6 For listed buildings or homes in conservation areas, check with your local planning authority before installing even a buried tank.7

Plumbing harvested water into toilets or a washing machine brings in the Water Supply (Water Fittings) Regulations 1999, which sit alongside the Building Regulations. The harvested water must be kept entirely separate from the drinking water supply, with any mains top-up through a proper air gap and the pipework clearly marked.8 Some of the work also has to be notified to your water company before it starts, including an automatic garden watering system.9 A WaterSafe-registered plumber will know what applies and handle the notice.

There is also a European standard, BS EN 16941-1 (on-site non-potable water systems, systems for the use of rainwater), which covers the design, sizing, installation, identification, commissioning and maintenance of rainwater harvesting systems.10 The older British code of practice, BS 8515, was withdrawn in July 2018.11 The first edition, BS EN 16941-1:2018, was withdrawn in March 2024.12 The current edition, BS EN 16941-1:2024, was published in June 2024.10 Any reputable installer will design to this standard.

Are There Grants Available?

As of 2026, there is no national grant scheme in England specifically for domestic rainwater harvesting. However:

  • Some water companies offer water butt discounts or subsidies, check with your supplier
  • Green Homes Grant closed in 2021, and the energy schemes that followed, ECO4 and the Great British Insulation Scheme (closed March 2026), fund heating and insulation, not water1314
  • Scotland and Wales have occasionally offered local authority rebates, check with your local council
  • New build developments may be required by planning conditions to incorporate sustainable drainage (SuDS), which can include rainwater harvesting

Maintenance Requirements

Unlike solar panels, rainwater systems need regular attention; typical intervals, which vary by system and maker, are:

  • First-flush diverter, clean quarterly (removes first-flush contaminants such as bird droppings and particulates)
  • Calmed inlet filter, clean every six months
  • Tank interior, inspect annually; clean every three to five years
  • Pump, service per manufacturer’s schedule, typically every two years

Annual maintenance costs run to £100–£200 if carried out by a contractor, or much less if the homeowner is comfortable doing visual checks and filter cleaning themselves.

Is It Worth It for Your Home?

A rainwater harvesting system makes most sense if you are:

  • Building a new home (integrate the tank during groundworks for the lowest cost)
  • Carrying out a major extension or landscaping project where excavation is already planned
  • A heavy water user, large garden, pool, or frequent laundry
  • In a metered water area with high tariffs
  • Motivated by environmental impact as much as payback

For most retrofits on average water users, a water butt for the garden plus conscious behaviour change (shorter showers, full washing machine loads) will deliver better value per pound spent. But if the conditions are right, a properly designed underground system is a durable, low-visibility improvement that reduces your environmental footprint and hedges against rising water tariffs for decades.

References (14)

Figures in this note were checked against the sources below on 2 October 2026. Superscript numbers in the text point to them. Every source the site cites, by topic.

  1. 1technicalvery strongMet Office, guidance.RN-8Q8XJ7The Met Office's official annual rainfall series for England. The 30 annual totals for 1991 to 2020 average 869.6 mm.
  2. 2technicalvery strongEnvironment Agency (GOV.UK), guidance.RN-MZW3RPThe Environment Agency's account of the 2025 drought in England records that by the end of the summer nearly 9 million people were under a hosepipe ban (temporary use ban).
  3. 3technicalfairEnvironment Agency (hosted by Waterwise), guidance.RN-BIY7MZThe Environment Agency's 2010 guide to domestic rainwater harvesting. Its case studies found 40 to 50 per cent reductions in mains water use against homes without a system.
  4. 4technicalfairConsumer Council for Water (CCW), guidance.RN-WQX5Y4The statutory water consumer body's page on household water use: about 139 litres per person per day, with typical volumes for showers, toilets and appliances.
  5. 5technicalfairThames Water, guidance.RN-9HR8XRThames Water's page for metered household customers, giving the 2026–27 volumetric charges for clean water and wastewater per cubic metre.
  6. 6technicalvery strongThe National Archives (legislation.gov.uk), legislation.RN-J6L7TIThe primary legal text for garden rooms, sheds, summerhouses, pergolas, greenhouses and outdoor pools. Class E permits any building or enclosure, swimming or other pool within the curtilage required for a purpose incidental to the enjoyment of the dwellinghouse, plus a domestic heating oil container. Limitations: E.1(b) buildings, enclosures and containers other than the original dwellinghouse must not cover more than 50% of the curtilage; E.1(c) nothing forward of a wall forming the principal elevation of the original dwellinghouse; E.1(d) single storey only; E.1(e) maximum height 4 metres with a dual-pitched roof, 2.5 metres if any part is within 2 metres of a curtilage boundary, otherwise 3 metres; E.1(f) eaves no higher than 2.5 metres; E.1(g) not within the curtilage of a listed building; E.1(h) no verandah, balcony or raised platform; E.1(j) oil containers capped at 3,500 litres. E.4 defines incidental use as including keeping poultry, bees, pet animals, birds or other livestock for domestic needs or personal enjoyment, which is why a garden room used as a separate dwelling falls outside Class E.
  7. 7technicalvery strongThe National Archives, legislation.RN-OWGIY3Schedule 2 Part 1 of the GPDO 2015, development within the curtilage of a dwellinghouse. This is permitted development itself: Class A enlargement and alteration, with the limits and conditions, through the classes covering roof alterations, porches, outbuildings and hard surfaces. Every statement about what can be built without planning permission traces to this Part, and the exclusions at the start of each class are where most projects actually fall out.
  8. 8technicalvery strongThe National Archives, guidance.RN-MY6E6ESchedule 2 to the Water Supply (Water Fittings) Regulations 1999, which applies in England and Wales. It caps WC flush volumes and requires backflow prevention on every water system.
  9. 9technicalvery strongThe National Archives (legislation.gov.uk), guidance.RN-29CES1Regulation 5 of the Water Supply (Water Fittings) Regulations 1999: the work that must be notified to the water undertaker, and consented, before it begins, including large baths, pumps drawing over 12 litres a minute from a supply pipe, reverse osmosis and water treatment units, automatic garden watering systems and deep or shallow external pipework.
  10. 10technicalstrongBSI Knowledge, guidance.RN-SE7L2YBSI's page for the current BS EN 16941-1:2024 gives its scope: design, sizing, installation, identification, commissioning and maintenance of rainwater harvesting systems for non-potable use.
  11. 11technicalstrongBSI (British Standards Institution), a standard.RN-P0GUENThe British Standard for rainwater harvesting, the reference a note on collecting and reusing rainwater needs. Published 31 Jan 2009 and withdrawn 19 Jul 2018, so cite it as the established code rather than a current one. Its scope gives recommendations on the design, installation, testing and maintenance of rainwater harvesting systems supplying non-potable water in the UK. It covers systems supplying water for domestic uses in residential, commercial, industrial or public premises that do not require potable water quality, and it names those uses explicitly as laundry, WC flushing and garden watering. That scope is the key point for a homeowner: harvested rainwater is fluid category 5 under the Water Supply (Water Fittings) Regulations 1999 and must not be connected to drinking or washing supplies, so the standard's non-potable limitation is a legal boundary as well as a design one.
  12. 12technicalstrongBSI, guidance.RN-DTC5N1BSI's catalogue entry for BS EN 16941-1:2018: its scope (design, sizing, installation, commissioning and maintenance of rainwater systems) and its withdrawal on 22 March 2024.
  13. 13technicalvery strongOfgem.RN-RDOIJRThe scheme, formerly known as ECO+, ran from April 2023 to 31 March 2026 and is now closed. It obliged medium and large energy suppliers to deliver measures reducing energy use in the least energy-efficient homes in Great Britain. Eligibility was homes with an EPC rating of D to G in Council Tax bands A to D in England, or A to E in Scotland and Wales, plus low-income and vulnerable households. Unlike ECO4, which funds whole-house packages, GBIS mostly delivered a single insulation measure per home. This is the page to cite when a note has to say a grant route has closed rather than leave a reader chasing it.
  14. 14technicalvery strongDepartment for Energy Security and Net Zero (GOV.UK), guidance.RN-40OD16The withdrawn GOV.UK guidance for the Green Homes Grant voucher scheme, confirming it closed to applications on 31 March 2021 and funded energy efficiency measures.

  1. UK and regional series: England rainfall, annual totals from 1836, Met Office, accessed 30 September 2026. metoffice.gov.uk

  2. 2025 drought: how it developed in England, Environment Agency (GOV.UK), accessed 2 October 2026. gov.uk

  3. Harvesting rainwater for domestic uses: an information guide, Environment Agency (hosted by Waterwise), accessed 30 September 2026. database.waterwise.org.uk

  4. How much water do you use?, Consumer Council for Water (CCW), accessed 30 September 2026. ccw.org.uk

  5. Metered customers, Thames Water, accessed 30 September 2026. thameswater.co.uk

  6. The Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1, Class E, The National Archives (legislation.gov.uk), accessed 30 September 2026. legislation.gov.uk

  7. The Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1, The National Archives, accessed 14 September 2026. legislation.gov.uk

  8. The Water Supply (Water Fittings) Regulations 1999, Schedule 2: Requirements for water fittings, The National Archives (legislation.gov.uk), accessed 30 September 2026. legislation.gov.uk

  9. The Water Supply (Water Fittings) Regulations 1999, regulation 5: Notification, legislation.gov.uk, accessed 29 September 2026. legislation.gov.uk

  10. BS EN 16941-1:2024 On-site non-potable water systems. Systems for the use of rainwater, BSI Knowledge, accessed 2 October 2026. knowledge.bsigroup.com

  11. BS 8515:2009+A1:2013 Rainwater harvesting systems. Code of practice, BSI Knowledge, accessed 2 October 2026. knowledge.bsigroup.com

  12. BS EN 16941-1:2018 On-site non-potable water systems. Systems for the use of rainwater, BSI, accessed 30 September 2026. knowledge.bsigroup.com

  13. Great British Insulation Scheme, Ofgem, accessed 2 October 2026. ofgem.gov.uk

  14. Green Homes Grant: make energy improvements to your home (closed), Department for Energy Security and Net Zero (GOV.UK), accessed 30 September 2026. gov.uk