Greywater
In plumbing · also called Grey water
Lightly used water from baths, showers and basins. A reuse system can treat it and use it for WC flushing, but it goes off quickly if stored, so surplus goes to the foul drain. Kitchen sink water is usually left out.
Using Greywater in a plumbing system
Updated
A distinction worth remembering
Fix leaks and choose efficient fittings before reaching for reuse. Where rainwater or greywater is reused, treat it as a separate, non-drinking supply: a protected mains top-up, marked pipework and no link to the drinking water.
Questions to take further
- Do I need permission for rainwater harvesting?
- In England and Wales the water undertaker is given notice before a harvesting system is installed, and it can attach conditions. A water butt filled from a downpipe and emptied by hand is not connected to the plumbing, so it needs no notice.
Sources
- GOV.UK: Approved Document G (water efficiency) — Guidance for England on the water efficiency figure for new dwellings and the two ways of showing it is met; guidance is not itself the legislation.
- Water Regs UK: notification — When the water undertaker must be told before plumbing work, including a new rainwater harvesting system, and how consent works.
- Water Regs UK: backflow protection — Contamination risks and why protection must match the fluid category and conditions.
Where Greywater fits in the learning path
The Rainwater, Maintenance and Environmental Protection section covers these topics:
- Rainwater Gutters and Downpipes
- Water Efficiency and Reuse
- Maintenance and Environmental Protection
Read, practise, return
1. Read it in context
- Water Efficiency and ReuseRainwater, Maintenance and Environmental Protection
2. Try recalling, then explore practice
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3. Return to the meaning
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Recall a related term
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A system that collects rain from a roof, filters and stores it in a tank, and pumps it to WCs, the garden and sometimes a washing machine. It is not drinking water, and its mains top-up is protected against backflow by an air gap.
Rainwater harvesting
Read the Rainwater harvesting entryCompare related terms
Open a meaning to compare its role with Greywater, or follow its full entry.
Rainwater harvesting
A system that collects rain from a roof, filters and stores it in a tank, and pumps it to WCs, the garden and sometimes a washing machine. It is not drinking water, and its mains top-up is protected against backflow by an air gap.
Read the Rainwater harvesting entryFluid category
A scale of five categories that grades water by the harm it could do if it flowed back into drinking water. Category 1 is wholesome drinking water and category 5 is the most serious risk, such as water that may contain human waste. The higher the category, the stronger the backflow protection needed between that water and the supply.
Read the Fluid category entryBefore you start: some plumbing work is regulated or notifiable
Some water fittings work needs notice to, and consent from, the water supplier before it starts. Check the rules where you live.
Gas work is for competent workers covered by a Gas Safe registered business in Great Britain. Northern Ireland has separate gas regulations. Do not work on gas pipes or appliances yourself.
In England, installing an unvented hot-water system over 15 litres is notifiable building work: use a competent installer registered with a competent-person scheme, or tell building control before work starts. Leave this work to a suitably skilled person.
Wales, Scotland and Northern Ireland have their own water and building rules; check which apply before work starts. Electrical connections belong with an electrician.
This guide does not qualify you or make you competent, approved or registered for plumbing, gas or unvented work.
A definition is a start. Using it in a real question is where it sticks.