What does a greywater system cost in the UK in 2026
If you are on a metered water supply and looking to cut your bills, a greywater system can reuse water from baths and showers for toilet flushing and garden watering. But the upfront cost is significant and payback is slow.
A greywater system costs £1,500–£5,000 installed in the UK in 2026. Payback takes 7–15 years for metered homes, while unmetered households see no savings. Compare system types to find the best fit.
- Installed cost ranges from £1,500 for manual diverters to £5,000 for full treatment systems.
- Payback takes 7–15 years for metered homes; unmetered homes see no financial return.
- Annual water saving is 20–75 m³ depending on system type and household size.
- Retrofitting to existing plumbing adds £500–£1,000 and extends payback by 2–4 years.
- Energy Saving Trust data shows 30–40 litres per person per day can be reused.
- What does a greywater system cost in the UK in 2026
- Quick numbers greywater system costs, savings, and payback
- How a greywater system works and what it replaces
- How much a greywater system saves on your water bill
- The three main types of greywater system and their installed costs
- Is a greywater system eligible for any UK grants or schemes in 2026
- How to verify an installer and what certification is required
- The direct answer what a greywater system actually costs in the UK in 2026
A residential greywater system costs £1,500–£5,000 installed, with payback typically taking 7–15 years for metered households. Unmetered homes see no direct financial return at all.
Quick numbers greywater system costs, savings, and payback
| System type | Installed cost (incl. VAT) | Annual water saving (m³) | Annual bill saving (metered) | Payback period |
|---|---|---|---|---|
| Manual diverter (gravity) | £1,500–£2,000 | 20–30 m³ | £80–£130 | 12–18 years |
| Basic pump-and-filter system | £2,500–£3,500 | 30–50 m³ | £130–£200 | 13–18 years |
| Full treatment system (UV + membrane) | £4,000–£5,000 | 50–75 m³ | £200–£350 | 12–18 years |
| Retrofit to existing plumbing | Add £500–£1,000 | Varies | Varies | Extends payback by 2–4 years |
Sources: Energy Saving Trust “Water energy savings” factsheet 2025/26 (Energy Saving Trust, 2026); Ofgem typical domestic consumption values (TDCVs) 2026 (Ofgem, 2026).
How a greywater system works and what it replaces
Greywater is wastewater from baths, showers, and hand basins — not toilets, kitchens, or washing machines — collected and reused for toilet flushing and garden irrigation. A diverter valve sends this water to a holding tank instead of the main drain.
Basic systems require you to manually switch between drain and reuse. Automated systems treat the water with filtration and ultraviolet (UV) light before storing it. The system replaces the equivalent volume of mains water for those uses, typically 30–40 litres per person per day in a UK home, according to Energy Saving Trust data (Energy Saving Trust, 2026).
No structural changes to internal pipework are needed for a diverter. Full treatment systems require a separate supply pipe to toilets and outdoor taps, which adds installation complexity and cost.
How much a greywater system saves on your water bill
A metered household of four with a full treatment system can save 50–75 m³ per year, worth £200–£350 annually at 2026 average water and sewerage rates, based on Ofgem typical domestic consumption values (Ofgem, 2026). Manual diverters save less — approximately 20–30 m³ per year — because they cannot treat water for toilet flushing without manual intervention.
Sewerage charges are avoided on reused water, typically 50–60% of the total water bill saving, according to Ofwat’s “Water and sewerage charges” report 2025–26 (Ofwat, 2026). Unmetered households save nothing financially; the system only reduces environmental impact and is not cost-justified on bill savings alone.
The three main types of greywater system and their installed costs
Manual diverter: £1,500–£2,000 installed. This is a valve and storage tank that requires you to switch between drain and reuse. No treatment, so water can only be used for garden irrigation within 24 hours.
Basic pump-and-filter system: £2,500–£3,500 installed. Includes a pump, coarse filter, and small holding tank. Treats water for toilet flushing but not for storage longer than 24 hours.
Full treatment system with UV: £4,000–£5,000 installed. Multi-stage filtration, UV sterilisation, and a larger tank. Water can be stored for up to 7 days and used for both toilets and garden.
Retrofit cost to existing plumbing: Adds £500–£1,000 for new pipe runs to toilets and outdoor taps, based on MCS installer survey data 2026 (MCS, 2026).
Is a greywater system eligible for any UK grants or schemes in 2026
No specific national grant covers greywater systems alone. The Boiler Upgrade Scheme (BUS) and ECO4 are for heating and insulation only (GOV.UK, 2026).
Some local authorities offer water-efficiency grants of £200–£500 for greywater diverters. Check your council’s website or contact the Energy Saving Trust regional advice line (Energy Saving Trust, 2026). Water companies in water-stressed areas — such as Anglian Water, Southern Water, and Thames Water — may offer rebates or free water-saving devices, but full greywater systems are rarely covered.
VAT is charged at the standard 20% rate. Greywater systems are not on the list of energy-saving materials eligible for reduced 5% VAT (HMRC VAT Notice 708/6, 2026 edition) (GOV.UK, 2026).
How to verify an installer and what certification is required
All greywater systems connected to mains drainage must be installed by a competent person registered with a government-approved scheme. For electrical connections (pumps, UV units), the installer must be registered with NICEIC or NAPIT for Part P compliance (GOV.UK, 2026).
For plumbing connections, Gas Safe Register is not relevant. Look for TrustMark-registered plumbers or those holding WaterSafe accreditation (TrustMark, 2026). MCS certification is not required for greywater systems; MCS covers microgeneration (solar, heat pumps), not water reuse (MCS, 2026).
Always request a written quote that itemises system cost, installation labour, and any structural pipework. Check the installer’s public liability insurance covers water damage.
compare greywater system vs rainwater harvesting costs
The direct answer what a greywater system actually costs in the UK in 2026
For a typical three-bedroom semi-detached home with a family of four on a metered water supply, a basic manual diverter costs £1,500–£2,000 installed and saves £100–£150 per year on water bills. A full treatment system costs £4,000–£5,000 installed and saves £200–£350 per year.
Payback for the diverter is 10–15 years; for the full system, 12–18 years. Neither is a short-term financial win. Financial return only exists for metered households; unmetered homes see zero bill savings.
The primary justification is environmental: reducing mains water consumption by 30–50% and lowering the household’s water footprint, not financial payback (Energy Saving Trust, 2026).
how to reduce water bills without installing a greywater system
Frequently Asked Questions
A residential greywater system costs £1,500–£5,000 installed, according to Energy Saving Trust 2025/26 factsheets. Manual diverters start at £1,500, while full treatment systems with UV and membrane filtration cost up to £5,000.
No, unmetered homes see no direct financial return from a greywater system. The payback is only possible on a metered water supply, as bills are based on usage rather than a fixed rate.
A greywater system saves 20–75 m³ of water annually, depending on the type. Manual diverters save 20–30 m³, while full treatment systems save 50–75 m³, based on Ofgem typical domestic consumption values for 2026.
Payback typically takes 7–15 years for metered households, according to Energy Saving Trust data. Manual diverters have a payback of 12–18 years, and full treatment systems 12–18 years, depending on water usage and system cost.
Yes, retrofitting to existing plumbing adds £500–£1,000 to the installation cost. This extends the payback period by 2–4 years, as noted in the Energy Saving Trust factsheet for 2025/26.
A greywater system replaces mains water used for toilet flushing and garden irrigation. It reuses wastewater from baths, showers, and hand basins, reducing metered water bills by £80–£350 per year.
