Can you water plants with grey water, pool or hot tub water?
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Part of our garden and rainwater guide
The shower takes an age to warm up, the washing-up bowl is full and the lawn has gone brown. Can that water go on the plants, and what about the hot tub? You can check pH, hardness and chlorine in your own water with a 20-in-1 test strip.
Short answer: Yes, ideally on ornamental plants and when rainwater has run out. The RHS lists showers, baths, washing machine rinse cycles and kitchen sinks as grey water, says to use it straight away and not store it beyond 24 hours unless filtered, and to alternate it with rainwater or mains water to avoid salt build-up.
By Andrew Tomlinson, WaterKit · Last reviewed 29 October 2026
What is grey water?
It is household water that has already been used for washing. The Royal Horticultural Society (RHS) lists water from showers, baths, washing machine rinse cycles and kitchen sinks. nidirect in Northern Ireland calls it any water used in the home except water from toilets, and says water used outdoors can reach 50 per cent of the total in hot, dry weather.
What suits a plant depends on what is in the water, and you can check a few things such as pH, hardness and chlorine yourself with a 20-in-1 test strip. The Drinking Water Inspectorate (DWI) published a March 2026 expert group report on governing non-drinking water from rainwater harvesting and greywater reuse systems. We have not drawn figures from it for this guide.
Can you water plants with grey water?
Yes, mainly on ornamental plants, and the sources attach conditions. The RHS says grey water is best kept off edible crops, and the table sets out what each source says.
| Source | What it says |
|---|---|
| RHS, collecting and reusing water | Ideally use grey water only on ornamental plants. If used on edible crops, limit it to crops that will be cooked, so not salads |
| nidirect | Shower, sink and laundry water can be reused in the garden during droughts. Bath and shower water suits non-edible plants. Make sure it is cool and do not pour it straight onto foliage |
| RHS, heatwave advice | Water lightly used for washing, bathing and in paddling pools counts as greywater. It can be used when rainwater stores are exhausted, but exclusive use over a long period can lead to saline build-up |
We found no single UK-wide rulebook for hand-watering with grey water in the sources we read, so each statement above is attributed.
How should you use grey water?
Straight away, with a watering can, says the RHS. Its list is below.
- Avoid water containing bleach, disinfectants, dishwasher salt or harsh cleaners.
- Do not store it longer than 24 hours unless it is filtered through a reed bed, a sand filter or a professionally designed water treatment system.
- Apply it with a watering can, because grease and fibres can clog irrigation systems.
- Alternate it with rainwater or mains water to avoid a build-up of mineral salts in the soil. Our water butt guide covers collecting the rainwater.
For anything plumbed in, England's building regulation Approved Document G (last updated 1 October 2024) covers cold and hot water systems and water efficiency in buildings, so ask an installer before changing any pipework.
What one reader found
A forum poster described reusing grey water during the July 2018 heatwave. Having redesigned their garden that spring, they wrote that their 800 litres of water butt supply was "long gone", so they turned to shower, bath and washing machine water. Siphoning the bath through a window with pumps was fiddly, since one pump's valve end snapped off and a cheap fuel siphon was slow. An ordinary garden hose with a tap attachment worked best and emptied the bath in about 5 minutes into a rainwater butt raised about 30cm off the ground. Seep and soaker hoses did not work because soap clogged the holes, while drip irrigation did. That matches the RHS warning that grease and fibres can clog irrigation systems. It is one person's experience, not official advice. Shared on MoneySavingExpert Forum
Why might your own water not suit your plants?
Because what is in mains water depends on where you live and on what your home does to it. The RHS says the minerals in mains water, especially in hard water areas, can raise soil pH and affect nutrient availability, and that rainwater is naturally soft and low in minerals. In its houseplant guide it adds that hard tap water is alkaline, which acid-loving plants do not like, and that chlorine in tap water can affect some plants, so it advises letting tap water stand in an open container for at least 24 hours. Its spider plant guide says the fluoride in tap water can brown leaf tips.
The area figure is an average. Your tap may be fed through a water softener, which the RHS says removes calcium and magnesium and replaces them with sodium. The RHS says softened water is good for short-term use but not recommended in the longer term, because sodium can build up in soil and affect nutrient availability. In our view, grey water from a softened home will carry that sodium with it. The RHS houseplant guide goes further and says the salts in domestic water softeners should never be used to water houseplants. A figure for the area does not tell you what comes out of your own tap. You can look up your local hardness with our how hard is my water guide, and we found no local figure for garden water in the sources we read.
“An area figure is only an average, so I would not assume it describes your own tap, especially if you have a water softener, because that changes what ends up in your grey water”
If chlorine is the worry, our guide to removing chlorine from tap water covers standing and other methods, and a strip can indicate whether the chlorine pad reading changes after standing, though a level below the first step of 0.5 mg/L reads as zero either way.
Can you water plants with pool or hot tub water?
The sources we read for this guide do not say. They contain no chlorine level for plants and no advice on emptying a swimming pool or hot tub onto a garden, so we give none. The RHS says water lightly used in paddling pools counts as greywater, and that chlorine in tap water can affect some plants. Our hot tub chemicals guide covers what tub water contains. The sources we read give no guidance on putting salt-water pool water on plants.
How can you check your water before it goes on the plants?
A strip can indicate pH, hardness, sodium chloride and chlorine in a glass of the water, to set beside your tap. The WaterKit Water Test Kit is made for drinking water and we have not validated it on grey water. Fill a clean glass or cup, dip one strip, wait 30 to 60 seconds and match the pads to the chart, or enter the colours in our free results checker (see how to test your water at home). The last column is our own reading of the chart steps. Where the middle column says we found no figure, that means in the sources listed below.
| Check | What the UK sources say | Our strip chart |
|---|---|---|
| pH | The RHS says rainwater has the right pH for most plants. We found no UK official pH range for water used on home garden plants | Steps at 6.2, 6.8, 7.2, 7.6, 7.8 and 8.4. This is the water, not the soil, and we give no verdict on a reading |
| Hardness | The RHS says hard tap water is alkaline. We found no UK official hardness figure for grey water | Steps at 0, 25, 50, 100, 250 and 425 mg/L, with no stated calcium carbonate basis |
| Sodium chloride | The RHS warns of mineral salt build-up. We found no UK official salt figure for watering a home garden | Steps at 0, 100, 250, 500, 1000 and 2000 mg/L, indicative only. A high step would indicate a salty sample, not where the salt came from |
| Chlorine | The RHS says chlorine in tap water can affect some plants. We found no UK official plant limit | Steps at 0, 0.5, 1, 3, 5, 10 and 20 mg/L. A zero means none seen at the first step, not none present |
A useful comparison is tap water against the same water after standing 24 hours, or tap against grey water on the same day. Three things are outside what the kit can do.
- No pad shows soap, detergent or cleaning products, and the sources we read give no UK official standard for grey water on home garden plants to compare a reading with. The fluoride pad starts at 4 mg/L, so it is not a check for the tap-water fluoride the RHS mentions for spider plants.
- The optional rapid bacteria test is a coliform presence screen for drinking water. We do not claim it for grey water.
- A strip result has no legal standing and does not replace the RHS conditions above.
The area figure is an average, and your own tap may differ, for example if a water softener feeds it, since the RHS says softeners replace calcium and magnesium with sodium. The pads that matter here are pH, hardness, sodium chloride and chlorine. A higher sodium chloride step in your grey water than in your tap would indicate a saltier sample, and a chlorine pad that reads lower after 24 hours of standing would indicate the chlorine is dissipating. Best pack: 20 strips, enough for several side-by-side checks of tap, stood and grey water through a dry spell, £5.99 (or £10.99 with a bacteria test for your drinking water), with free 2nd Class delivery on every order. See the kit
Your grey water questions
How to filter grey water for garden use?
The RHS names a reed bed, a sand filter or a professionally designed water treatment system for keeping grey water beyond 24 hours, and gives no design. We give no filtering instructions.
Is pond water good for plants?
nidirect says to use excess pond water on the lawn or to water garden plants, to avoid spreading invasive pond plants into waterways, and to avoid damp areas. It does not say whether the water suits plants. The RHS says to avoid water from uncovered dipping tanks on seedlings and young plants, as it can stagnate. For clearing a pond, see how to keep pond water clear.
Will washing machine water kill plants?
The RHS lists washing machine rinse cycles among usable grey water, and says to avoid water containing bleach, disinfectants or harsh cleaners.
How to save shower water for garden?
The RHS says to use it straight away and not store it beyond 24 hours unless filtered. It does not explain how to collect it.
Can you use shower water for plants?
Yes, say the RHS and nidirect, which says bath and shower water suits non-edible plants if cool and not poured onto foliage.
Can you use dishwasher to water plants?
The RHS says to avoid water containing dishwasher salt or harsh cleaners. We found nothing in the sources we read on dishwasher outlet water in particular.
Is filtered water good for plants?
The RHS suggests rainwater or filtered water for spider plants, because the fluoride in tap water can brown leaf tips. Its guide to collecting and reusing water says purified water, such as distilled or deionised water, can help plants that need very soft water, such as orchids, when rainwater is unavailable, but fertiliser then needs adding because it lacks minerals.
Will hot tub water kill grass?
The sources we read give no figure or advice for grass. See the pool and hot tub section above.
Can I use hot tub water on the garden?
We found no guidance on this in the sources we read, so we do not give a chlorine level for plants.
Can you use pool water to water plants?
The same applies to swimming pools. The RHS counts water lightly used in paddling pools as greywater, and that is the only pool-related statement in our sources.
Is rainwater better for plants?
The RHS says rainwater is the best option for garden watering, being naturally soft, low in minerals and with the right pH for most plants. It says to avoid using stored water on seedlings, because it may carry damping-off diseases.
Is rusty water bad for plants?
We found no guidance on rusty water for plants in the sources we read. Our brown or cloudy water guide covers rust-coloured tap water.
How to test ph of water for plants?
Our strip's pH pad has steps from 6.2 to 8.4 (see the table above) and we give no verdict on a reading. The RHS says soil pH testing kits are widely available in garden centres and online.
Sources
- Royal Horticultural Society, Collecting, storing and reusing water (undated; grey water list and rules, softened water, rainwater as best option, mains minerals and soil pH; read 29 October 2026).
- Royal Horticultural Society, How to reduce your water use during a heatwave (undated; greywater including paddling pools, saline build-up; read 29 October 2026).
- Royal Horticultural Society, How to grow houseplants (undated; hard water, chlorine, standing 24 hours; read 29 October 2026).
- Royal Horticultural Society, How to grow spider plants (undated; fluoride, leaf tips, rainwater or filtered water; read 29 October 2026).
- nidirect, Saving water in the garden (undated; greywater definition, 50 per cent outdoor use, bath and shower water on non-edible plants; read 29 October 2026).
- nidirect, Invasive non-native aquatic plants (undated; waste pond water on the lawn or garden plants; read 29 October 2026).
- Ministry of Housing, Communities and Local Government, Sanitation, hot water safety and water efficiency: Approved Document G (first published 3 March 2010, updated 1 October 2024; read 29 October 2026).
- Drinking Water Inspectorate, Governance framework for non-drinking water from rainwater harvesting and greywater reuse systems: Expert Group recommendations (March 2026; read 29 October 2026, title and date only).
- MoneySavingExpert Forum, Grey water recycling for the garden during the heatwave (a forum post of 22 July 2018, one person's experience and not official advice; read 29 October 2026).
- WaterKit, Water Test Kit (20-in-1 strip, 30 to 60 second read, optional rapid coliform test read after 24 to 48 hours, free 2nd Class delivery on every order) and results portal. The strip-chart column and comments on expected readings are WaterKit's own reading of the colour chart steps.
Contains public sector information licensed under the Open Government Licence v3.0.