Let it rain

Only a small frac­tion of farmers, gardeners and wine­makers use the rain­water falling on their farm and roof surfaces to irri­gate their crops or as drinking water. The mindset plays a greater role here than economic calcu­la­tions.

“We’re sensi­tive when it comes to water”, says wine­grower Andreas Hemer from Worms-Aben­heim in southern Germany. And for good reason: the annual rain­fall in this region is a measly 550l/m2. He and his brother Stefan there­fore use effi­cient drip irri­ga­tion in times of drought on their organic vine­yard. In 2012, the family busi­ness, with 36ha of vines and its own bottling station, built a new produc­tion hall outside the village centre. The devel­oped area comprises about 1ha, of which around 2,000m2 is covered by a roof, which is fitted with photo­voltaics on its sun-facing side.

Thinking long-term

“We want to collect the rain­water falling onto the roof in two large 50,000l cisterns”, explains Andreas Hemer. This water will be used mainly for mixing organic pesti­cides and to irri­gate the hedges planted around the winery grounds. Rain­water that flows over the paved surfaces later seeps into a trench dug around the grounds.

Of course, another option would be to drill a well on the prop­erty, but this would mean drilling 80 to 100m deep. This isn’t cheap, according to Andreas Hemer, not to mention the strain it puts on the ground­water balance. However, the planned rain­water processing is not an invest­ment that will pay off quickly.

“We’re thinking long-term. We’d like to supply our water ourselves as far as possible, similar to how we source our energy from wood­chip heating and our elec­tricity from photo­voltaics”, he says. The Hemer brothers converted their farm to organic oper­a­tions in 2003 and they are currently a member of the Ecovin asso­ci­a­tion of organic wine­makers. Further­more, the less waste water from the farm that ends up in the public sewage system, the lower the fees for the energy-inten­sive treat­ment of this water.

We’d like to supply our water ourselves as far as possible.

Andreas Hemer

Rain­water as drinking water?

Speaking of energy, more and more experts are pointing out the strong link between water and energy, using the term “water-energy nexus” –  when energy consump­tion increases, so does the need for water. Every dairy farmer knows the vast quan­ti­ties of water required for cattle housed in the shed all year round. With a daily require­ment of more than 100l per high-perfor­mance animal, a 200-cow oper­a­tion accu­mu­lates a remark­able annual quan­tity of 7,300m3 of water. Cattle also usually consume drinking-quality water. What could be more logical than repur­posing the water collected on the stall roofs for the thirsty animals?

Large cattle herds are often housed in cowsheds all year round: their drinking troughs thus use high amounts of water.

But there are some concerns to consider. “Cows require the best-quality water”, according to Dr. Peter Pascher, Director of Agri­cul­tural Struc­ture and Regional Policy at the German Farmers’ Asso­ci­a­tion. Mr Pascher believes that there are many argu­ments against the use of rain­water, such as for hygiene reasons (i.e. bacteria, cont­a­m­i­nants and foreign substances). “Today, food produc­tion in Europe has very high quality require­ments which could be jeop­ar­dised by the use of rain­water”, Mr Pascher adds. “And dairy producers are aware of this”. He fears that inad­e­quate drinking water could also have far-reaching conse­quences for live­stock health.

Pioneers in horti­cul­ture

Whether it’s deco­ra­tive plants or vegeta­bles in glasshouses: healthy plants need a suffi­cient and regular amount of water.

While only a small propor­tion of live­stock farmers are working on long-term strate­gies for the local treat­ment of valu­able water resources, even with compa­rably low water costs and despite increas­ingly evident climate change, greater strides have clearly been made in horti­cul­ture. “Rain­water processing is now being imple­mented by many oper­a­tions”, notes Dr. Andreas Wrede gladly. Dr. Wrede, Lead Exam­iner at the Horti­cul­tural Centre of the Schleswig-Holstein Chamber of Agri­cul­ture, does not however deny that recy­cling without phytosan­i­tary treat­ment is not recom­mended – even though it is expen­sive. “Every­body is aware that water prices will rise in the future and that it will also become harder to build wells”, observes the horti­cul­ture expert.

Mr Wrede also proposes another argu­ment: “The use of rain­water has a further advan­tage. In contrast to hard tap water, rain­water comes for free and is also of a softer water quality, which has a posi­tive effect on plant growth”. Mr Wrede hopes that in future, even more horti­cul­tur­ists, wine­growers and farmers will adopt new ways to conserve ground­water resources.

Espe­cially as, in the face of a growing demand for food, there is no longer any doubt that agri­cul­ture, whether in Europe or else­where in the world, will need to handle water more effi­ciently in order not to upset the deli­cate water supply balance.

Thirsty plants

Green­house plants are quite thirsty: although it differs consid­er­ably depending on the plant, around 42m3 of water on average is required daily for 1,000m2 of cultivation. To scale reser­voirs for tree nurs­eries and other horti­cul­tural oper­a­tions appro­pri­ately, the following guide­line figures apply: During the annual vege­ta­tion period, tree nurs­eries produce around 2kg of fresh wood mass per container area of 1m2. This requires about 550l of water. In order to meet this need with winter rain­fall, an area of 1ha requires a reser­voir with a volume of 3,500m3.

If rain­water is also collected during the summer, the reser­voir volume could be reduced by up to a third with simul­ta­neous filtering, according to the calcu­la­tions of Andreas Wrede from the Horti­cul­tural Centre in Eller­shoop, northern Germany. It’s not just collecting water that’s impor­tant for the water cycle however, but also the type of irri­ga­tion. While a rota­tion sprin­kler uses around 100m3/ha and per day, drip irri­ga­tion requires only 20m3.

 

Further infor­ma­tion