Sustainable water use
RHS scientists explain how to future-proof UK gardens while in a water crisis
What does this target mean?
Previously, the RHS relied heavily on water taken from rivers and bore holes (blue water).Looking to the future, we know it will be important to retain even more rainfall (green water) within the landscapes by finding ways to innovatively incorporate water storage within RHS gardens soils, using rain garden techniques. We also need to find new ways to provide longer term storage of rainwater.
To date, we have done this by building large scale water storage within the landscape in Clear Lake at RHS Wisley and are repairing the leat at RHS Rosemoor.
Our climate is changing, and fast and it's throwing up many challenges for gardeners, especially in the way we manage water. England is facing a deficit of five billion litres per day in water supply, and a further one billion for agriculture and industry by 2055, so making better use of the rain when it arrives will help everyone. Reserves will become more restricted as water becomes more scarce in the future.
As we move our gardens to rely more on green water (rainfall) and less on blue water (mains water), we must factor in expected changes to the seasonality of rainfall - wetter winters and drier summers with more extremes, which leads to drought and flooding situations. Therefore the timing of how we manage water is more important so we can prepare for greater levels of wet and dry soil.
Sustainable water use is all about balancing the amount of water we use, with the availability water sources, as efficiently as possible, so that we reduce our dependence on water taken from the environment. That means capturing, storing and using more rainwater, using less mains water, re-using water, watering efficiently and also creating less waste water.
What we have done so far?
All the RHS Gardens have already improved water management to help repair the water cycle. Ways we have improved water use efficiency and water management means we need to make changes to gardening practices and important infrastructural engineering developments. Here are some examples:
- RHS gardening practices have included only irrigating when necessary in the cool of the morning, sustainably managing grassed areas (less mowing and irrigation of certain areas), introduction of dry garden areas and increased
mulching - At RHS Wisley, we harvest rainwater from the RHS Hilltop building to an underground rainwater storage system (called Permavoid) which supplies water to the soil and plants growing above it using a wicking system, with the overflow water stored in Clear Lake to support summer irrigation of the Battleston Hill woodland landscape.
- RHS Wisley’s Clear Lake, coupled with rainwater harvesting at RHS Hilltop, can meet 70% of irrigation demand from plants on Battleston Hill This still needs testing through significant drought conditions.
- A rainfall harvesting model has been developed to assess the sufficiency of future water supplies for part of RHS Wisley and will be expanded to all sites.
- RHS Wisley has stopped drip-irrigating the orchard and started using automated rainwater harvesting systems from the Glasshouse Lake.
- Our first waterless toilet is being installed in the new learning garden at RHS Wisley.
- At RHS Bridgewater we installed a Sustainable Drainage System (SuDS) which uses plants to slow the flow of stormwater, which helps prevent flooding locally. So far the quantified water use by the system and the reduction in water discharge has reduced flood risk downstream.
- Rainwater harvesting from The Bridgewater Welcome Building and Plant Centre also avoids using mains water for some toilet flushing and irrigation.
- At RHS Hyde Hall in Essex, we have a 45 million litre reservoir to catch and store excess rainfall; big enough to ensure the garden minimises its routine use of mains water.
- At RHS Rosemoor in Devon, the garden’s lake is truly multipurpose, providing irrigation water, stormwater attenuation and a beautiful ornamental feature.
- RHS Harlow Carr in Yorkshire is one really big rain garden. The naturally moisture-retentive clay soils hold the rain, which slowly drains to the beck through the centre of the garden, and the nursery has recently refurbished rainwater harvesting systems. Swales around the refurbished Harrogate Arms rehydrate the landscape every time it rains.
These are just a few examples of our organisation-wide commitment to improved water management. In the future, we plan to capture and redirect water across whole garden landscapes to store more water in soil and further reduce reliance on water abstraction from the environment. To do this, water must be an integral factor in every piece of infrastructure we create, at every stage of planning, design and implementation.
What will the RHS do next to meet this target?
- The RHS will continue to better understand our water use, by improving metering, monitoring and analysis of water data.
- We have reduced our mains water use, by eliminating leaks and wastage, switching some tasks from mains to rains supply for horticulture, and implementing water efficiency measures.
- To safeguard the nation’s gardens, we have established a research programme to develop greywater reuse systems suitable for domestic gardens, and are investigating how to deploy greywater (recycled water) technology to our garden sites.
- We have created a water management plan for each RHS Garden, which assesses the current water and projected usage, sources of water available, any gap between supply and demand, and how to close those gaps. We have identified significant water-efficient appliances and rainwater harvesting, storage and reuse opportunities across all RHS sites.
- We’ll also aim to replenish supplies by harvesting and storing as much water as possible.
The way we garden will change dramatically over the next decade. We’ll need to be more flexible and adaptable in the face of a fast-changing climate
Why should gardeners care about this?
The spring of 2025 was recorded as the driest for 69 years, while 2022 and 2023 were the two warmest on record (from 1884). The number of ‘pleasant’ days has increased by 41% for the most recent decade, and warm days by 63%; hot days have more than doubled; and very hot days have more than tripled. These trends have impacts on gardening and water needs. While things are getting hotter, they are also getting wetter; five of the 10 wettest years on record have occurred in the 21st century, including an increase in heavy rainfall.
We will need to be more flexible and adaptable in the face of a fast-changing climate. The way we garden needs to change dramatically now.
Climate scientists have been predicting an increase in extreme weather events for a while, and now they’re unfolding before our eyes. Gardens and gardeners across the world are facing new challenges, including droughts and flooding in areas previously unaffected.
We know the climate is changing and weather extremes are more frequent, but we also know that gardens can help repair the water cycle. Green spaces hold excess rainfall in a flood and keep us cool in a dry spell, as plants and soils slowly evaporate the water held in soils to keep us cool. Rather than drawing on water resources that are already under pressure, gardens can contribute to relieving that pressure. Mulches reduce evaporation. Layered planting creates shade and holds in moisture. Watering at the right times maximises the efficiency of water use.
