Agricultural Buildings Show: Using barn roofs to cut your water costs

Collecting rainwater from barn roofs and using it for parlour and yard washing duties (where mains supply water is not necessary) isn’t a new concept.

“Farmers have always made use of some rainwater,” says Barrie Jackson of Receau, a Staffordshire company involved in commercial water harvesting and recycling systems.

“But the economic and environmental drivers behind water use have changed in the past few years and are now creating some urgency. Harvesting systems are seen as the way forward.”

Chief of these is the fact that water company charges are set to run at more than 4% above inflation for the five years between 2005 and 2010, due to OFWAT and the UK’s commitment to the EU Water Framework Directive, he reports.

“Water costs are increasing and will continue to do so. This has massive implications for most of the dairy farms in the country, as well as for others where water is used on a daily basis.”


On a dairy unit, typical water use is 120 litres a cow a day and mains water supply costs between £31 and £100 a cow a year, he adds. “It’s possible to recover about 40% of the farm’s water usage with a good rainwater harvesting system, so there are huge savings to be made.”

With rainwater harvesting, there’s a requirement for 24sq m of shed roof per cow, which means that each square metre of roof is worth between £1.50 and £4.50, he calculates.

On pig farms, all of the water usage can be recovered, while poultry units can expect to gain most of their drinking water and the entire amount needed for flood washing, advises Mr Jackson.

The other strong driver is the food chain’s interest in water footprints and environmental credentials. “The retailers have huge buying power and are now beginning to ask for evidence from farmers. Sainsbury’s, for example, has rainwater harvesting as one of its supplier criteria.”

Farmers interested in installing a rainwater harvesting system are entitled to grants and tax incentives, he says.

“There are a number of schemes available for encouraging the use of rainwater harvesting technology. Although eligibility is dependent on geographical location, up to 40% of the capital cost can be secured through grant assistance.”

Tax incentives, known as Enhanced Capital Allowances, also apply to farms investing in environmentally beneficial plant and machinery. They allow businesses to write off the whole cost of their investment against their taxable profits for the period in which they make the investment, he notes.

How it works

The first step with rainwater harvesting is a farm survey, which includes a feasibility study. From there, a system can be installed which includes either above- or below-ground water storage – always the most expensive part.

As the water hits the roofs, a preliminary filtration system is used to remove leaves and other debris, such as bird droppings. This water is then fed into a tank, where any floating debris and sediment is removed. The resulting “clean” water is then pumped out and can be used for a variety of tasks, although UV filtering is required to make it suitable for all farm use.

“Typically, the equipment needed for this would be £5000-6000 for a herd size of 200-300 cows. On a bigger unit, say with 1000 head of cattle, it would be £8000-10,000.”

This cost doesn’t include the water storage element, he admits. “Over the years, we’ve found that farmers have been very creative at finding storage. Most opt for above-ground storage.”

On all installations, Mr Jackson works on a payback time of two-and-a-half years. “Quite often it’s less than this.”

Funding help

Yorkshire Forward is helping farmers in Yorkshire and the Humber through their Farm Resource Efficiency Programme, which provides funding for equipment purchased to improve farm business resource efficiency.

For rainwater harvesting systems, this includes the costs of pumps, filtration systems, piping and storage tanks, of which 40% of the cost is eligible up to a maximum of £25,000, says Louise Hardcastle of Yorkshire Forward.

“Farmers have to submit an application showing how it is going to reduce their water costs, giving three estimates for the work and naming their preferred supplier,” she says.

A standard calculation template has been provided, simplifying the application process, she adds.

To date, 15 projects have received funding through the programme and there is growing interest in the scheme, she says.

  • You can find about your local RDA

Example costings

Example dairy farm – 90 milking cows in Cheshire

  • Metered water usage is 11,160 litres a day or 4.073cu m a year
  • Current water cost is £1.294/cu m or £5270 a year
  • Supply potential – total roof area of 2376sq m

Using Met Office rainfall figures plus coefficient of filtration/evaporation loss, the water supply from roofs is calculated at 2,352,000 litres a year or 2352cu m a year

  • Applications – yard and machinery washing
  • Recommendations – all the principal collecting shed and milk parlour roofs are suitable for harvesting rainwater, making it possible to filter and collect 58% of the farm’s requirement.
  • On current figures, this would save £3056 a year
  • Equipment cost – £10,250 + VAT

(If flushing out of parlour lines is not required, the equipment costs would fall by £3000 by excluding the need for UV and pre-filtration)

  • Storage costs – not included, but storage would be done in refurbished bulk storage tanks
  • Payback time is 33 months if UV included, or 24 months if not
  • Over a five-year period, the total charges for metered water would reduce by £19,957 (taking into account annual increases in water costs)

Where next?

Interested? The Milk Development Council suggests the following five steps for farmers considering rainwater harvesting.

  • 1 Find out your local rainfall data
  • 2 Calculate roof areas available for collection
  • 3 Consider what would be an acceptable return period for your business
  • 4 Work out the maximum you can afford to spend to achieve your target return or payback period.
  • 5 Work out your required storage size and cost your project.

Case Study: R.Harrison & Sons


Rainwater harvesting has been an integral part of the low-cost production system at R Harrison and Sons in West Sussex for the past nine years.

All the roof water from the buildings for 500 cows is collected and diverted to a purpose-built reservoir, from where it is pumped back through a pressurised system to the dairy buildings.

“We use it for all the cleaning jobs, such as washing down the parlour, and to supply all of our cattle drinking water,” says Charles Harrison.

“It isn’t used for jobs such as flushing out the lines, although that could be done with additional UV filtering.”

He estimates that it has saved the business a huge amount of money. “Before we got into this, we were spending more on water than we were on electricity.

“The amount of water needed by 500 cows is staggering and the cost of mains water has gone up considerably in the time that we’ve been catching roof water. And it’s never going to get any cheaper.”

Mr Harrison calculates that his rainwater harvesting system has paid for itself 10 times over since it was installed. “Fortunately, our main barn was suitable for the purpose. Our experience is that the capital cost is recouped within two-and-a-half years, but that does depend on the degree of specialisation.”

The costs of digging a reservoir were kept down by incorporating it with other work that was being done on the farm at the time. “Then we had to have about 1km of piping installed and the relevant pumps.”

Tests for bacteria are conducted on a regular basis to check the water’s suitability and prevent any contamination, he adds.

The rainwater passes through a sand filter, which has to be back-washed every week, but otherwise there is little management or maintenance required. “It’s straightforward and easy to do. No licences are required.”

He hasn’t had any questions on the farm’s water use from buyers, but points out that he did when the farm was reliant on a borehole. “Certainly, they have no quality or safety concerns. It will be interesting to see when they start asking about our water footprint.”

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