How water-efficient is a greenhouse?

Very, and through recovery rather than restraint. Water is dosed by drip to each plant, 20 to 40 percent drains through the slab by design to flush salts, and that drain is collected, disinfected and returned. Published discharge from Dutch substrate holdings is nought to ten percent of water supplied.

Why can't a greenhouse close its water loop completely?

Sodium. It is not a nutrient, the crop takes up almost none of it, and transpiration removes pure water — so it concentrates with every pass until discharge becomes unavoidable. No disinfection technique in common use removes it, which makes the limit chemical rather than technological.

How much water storage does a greenhouse need?

More than the legal minimum. Dutch law requires at least 500 cubic metres of rainwater storage per hectare, but modelling shows that volume still forces mains water and discharge in a dry year. Wageningen recommends well above it, and a larger basin buys years of avoided discharge.

Does recirculation solve greenhouse water emissions?

It solves the deliberate part. Leakage, drainage from soil-grown crops and crop-changeover cleaning water all leave the facility without passing any treatment step, and Wageningen ranks several of those above deliberate drain discharge for environmental load.

Greenhouse Water Use & Circularity

Recovery, not restraint

A greenhouse is not careful with water. It is circular.

Every plant gets its own dripper. Between 20 and 40 percent of what goes in drains straight through the slab — on purpose, to wash salts out of the root zone.

That drain is caught, disinfected and fed back in.

Published discharge from Dutch substrate holdings runs at nought to ten percent of the water supplied. Which means 90 to 100 percent of the drain goes round again.

No field crop comes close.

The thing that stops it being 100 percent is not equipment

It is sodium.

The plant barely takes any up. Transpiration lifts out pure water and leaves the salt behind. So every lap round the loop, the concentration climbs.

Eventually you have to dump and refill. Not because the water is dirty — the disinfection handles that — but because it is too salty to feed a crop.

And no treatment in ordinary use takes sodium out. This is chemistry, not a gap in the technology.

Which is why the water a site can actually draw shapes the whole design. Rainwater is nearly sodium-free. Well water in the wrong region is not.

Build the basin bigger than the law says

Dutch law asks for 500 cubic metres of storage per hectare.

That is a floor, and a low one. Modelling shows a basin that size still forces you onto mains water and into discharge in a dry year. Wageningen recommends well above it.

A bigger basin is dull capital that buys years of not having to dump. It is one of the few places in a greenhouse where the unglamorous option is simply the right one.

Say the honest version

Recirculation fixes the water you discharge on purpose. It does nothing about leakage, about drainage from soil-grown crops, or about the wash-down at crop change — and Wageningen ranks some of those above deliberate discharge for environmental load.

Saying that out loud is a stronger position than claiming a closed loop, because the people assessing your permit already know it.

DutchGreenhouses® designs the collection, treatment and recirculation chain around your source water and your rainfall, not around a legal minimum. Get in touch with a location and a water analysis.

From the knowledge base