Rainwater Harvesting in Agriculture
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What is Rainwater Harvesting?
Rainwater harvesting (RWH) is the collection and use of rainwater falling onto buildings which would otherwise have gone down the drains, been lost through evaporation, or soaked into the ground.
Buildings under construction present the ideal opportunity to install a RWH system – or it can be added to existing structures. A system may involve diverting drainage to a tank to collect water and if necessary, could include treatment to improve water quality for specific uses. Distribution pumps and pipes may also be required to supply the water to where it is needed on-farm.
Benefits of Rainwater harvesting – what’s in it for you?
Potentially, there are both economic and environmental benefits of rainwater harvesting.
- Typical charges for mains water are currently between £1 and £2 per cubic metre and are expected to rise in the future. Using RWH for some or all water use on-farm could reduce this expenditure, however savings will have to be offset against capital and operational outlay of the RWH equipment.
- Where water is discharged to a sewer, your water company will charge you a proportion of supply costs in your water bill for this discharge. Reducing your mains water use will ensure these additional savings can be made.
- Harvesting and using rainwater can reduce the quantity of water entering your slurry store, running across fouled yards, or entering your dirty water tank. This can mean a reduction in slurry store size and reduced amounts of dirty water to dispose of, resulting in cost savings.
- Rainwater does not contain treatment additives, such as chlorine, and is therefore considered by some to be better for irrigation. However, filtration and/or UV treatment may still for some crops.
- Rainwater is also considered better than mains water for spraying some crop protection products.
- RWH can reduce dependence on a supply from rivers and groundwater sources.
- RWH can also reduce the risk of localised flooding where water from large roof areas is not managed correctly.
- Other benefits may be particular to an individual farm such as better soil drainage, improved humidity levels and plant health.
A dairy farm with a 200 cow herd, has an annual water use of 11,300m3, approximating 7,300m3 for drinking, 2190m3 for milk cooling, and 1,825m3 for parlour washing.
The farm has a 3,000m2 roof area, and is in an area of 700mm annual rainfall and could therefore potentially harvest 1,680m3 of rainwater.
Some water will overflow the tank and some may be diverted as first flush from the roof. Assuming the farmer can store half of the 1,680m3 of rainwater, including payment for maintenance and pumping, the potential saving on a water utility bill at £1 per cubic metre could be approximately £400 using the harvested water for the parlour washing, or for animal drinking water. A farmer seeking 10 year payback could invest up to £4,000 in water harvesting.