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