Guidance on planning an on-farm irrigation reservoir

Abstracting from water sources is common in arable and livestock systems.

However, the practice is under intense scrutiny from regulatory bodies as water becomes scarcer, demand increases, and concerns grow about the impact of abstraction on priority habitats.

Securing a licence to draw from a river or underground source in arid months is, therefore, becoming more challenging.

See also: How to plan for water security and drought resilience

Regulatory bodies overseeing the licensing process are more likely to favour an application with a winter abstraction requirement.

That is why more farmers are investing in irrigation reservoirs, filling these during the wetter months to provide water when their crops most need it.

They are no small investment – depending on geology and whether a liner is needed, farmers can expect to pay £1,000-£3,000 per 1,000cu m to create the reservoir itself.

The supporting infrastructure, such as pipework, pumps and an electrical connection, can add hundreds of thousands of pounds more.

A reservoir, however, could increase the value of a farm, as the potential to irrigate means the land will have a greater earning capacity.

Brown & Co agricultural business consultant Andrew Spinks and planner Emma Griffiths, who have supported multiple on-farm irrigation projects, offer guidance on the process.

Assess the farm’s water requirement

Water demand is calculated according to cropping and land type. Cranfield University’s online tool, D-Risk, can be used to model different scenarios to calculate how much water is needed to serve the farm and how big the reservoir needs to be.

These can be specific to regional locations and the natural sources of water available.

Where some level of irrigation will be needed annually but the abstraction supply might be inconsistent, Andrew advises building a buffer into the calculations for reservoir size.

“In some cases, a farmer might not be able to abstract every year as they might have a great source of water for two years but not enough in the third, so it helps to factor in buffering capacity,” he says.

Consider topography

The build will be cheaper if the farm has clay soils, as there will be no requirement for a butyl liner.

“The ideal scenario is to dig a hole and find enough clay that can be manipulated to create a liner, but we quite often have farms that don’t have that and need to use a liner,” says Andrew.

It is important to work within the construction, design and management regulations on health and safety when creating a reservoir. These include appointing a principal designer and a contractor.

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Cost

Apart from the liner consideration, the total project cost will depend on variables associated with infrastructure.

“The pipework is very individual to each farm business. It will depend on how far the water needs to be moved from its source to the reservoir, what obstacles it needs to pass, and if there are road crossings, for example,” says Andrew.

“There is the pumping system to factor in, too, which again depends on the topography of the farm, and whether there is a ring main.

“Ideally, there will be an electrical connection. If not, the cost can be considerable. In some cases, running to a few hundred thousand pounds.”

The higher the value of the crop, the greater the economic benefit.

Co-operation

Collaboration between neighbouring farms can significantly reduce the financial burden, as not only can costs be shared, but the bigger the reservoir, the cheaper the unit cost.

Partnerships between farms with different rotations will also inject efficiency.

“An individual business won’t necessarily need to use all the water available because their rotation will vary from year to year, but if you have various farms accessing it, the water can be moved around more efficiently and it will make better use of it,” says Andrew.

In England, a new round of Local Resource Option funding, which encourages collaboration, is open for applications until 20 July 2025.

This is designed to enhance water resilience or supply for a small group of abstractors within an area.

Planning consent

Depending on the site and scale of the planned reservoir, development can fall within the scope of permitted development rights (PDRs) under the Town & Country Planning (General Permitted Development) Order 1995, subject to it complying with all relevant provisions.

A prior notification submission is required in all instances, and local planning authorities (LPAs) often require a subsequent prior approval submission, but they typically consider irrigation ponds positively, says Emma.

“Very often, prior approval is granted with relative ease, as a lot of technical information has informed the proposed reservoir from an early stage,” she says.

What the applicant must provide depends in part on the reservoir size – less than 1ha, and only technical surveys such as an ecology survey and details of flood risk and drainage engineering are required.

However, the overall requirement will be site-specific.

If the site is more than 1ha, it will trigger Environmental Impact Assessment (EIA) regulations and the need to seek a Screening Opinion from the LPA before submission of the prior notification.

“More often than not, this confirms that an EIA is not required,” says Emma.

Prior approval has a fixed fee which depends on the category the LPA deems the development to fall within, but “excavation” is the most likely and the fee for that, inclusive of a planning portal service charge, is £325.

If a reservoir has been created without following correct planning procedures, it will add significantly to the cost if the applicant attempts to secure permission further down the line.

“You can’t get prior approval retrospectively, so permission would then need to be sought under a full application, which will trigger the extra requirements associated with that,” Emma warns.

“The process for full planning applications, as opposed to prior notification, is more rigorous and the cost greater, especially so when you start to consider biodiversity net gain and the implications of that.”

This would be a consideration too if the scheme could not be delivered under a PDR.

The future of water sourcing

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Farmers are prohibited from using wastewater from treatment plants to fill reservoirs, but Brown & Co’s Andrew Spinks suggests that changing these rules could deliver solutions for agriculture, housebuilding and industry.

“Capacity in wastewater treatment plants is limiting housebuilding, so with more impetus from regulatory bodies and governments, economic growth could be unlocked and farmers would have a great source for irrigation,” he says.

“This system is commonplace in many countries, and it is entirely within our grasp.”

How farmers source water is under much greater scrutiny, particularly in drier regions such as the south-east of England, where demand from agriculture is competing with rapidly rising household and industrial requirements, and this will only amplify.

“Farms in certain circumstances are also going to have to think much more about how to save water and operate with less in the future, because demand will make it much more difficult to access water, not necessarily because the water isn’t there but because it will involve more management and infrastructure and the cost of doing that won’t warrant it for all scenarios,” says Andrew.

Defra will shortly publish its National Framework for Water Resources, setting out its approach in more detail.