# Irrigation > Part of: [Greenhouse Horticulture](/greenhouse-horticulture.md) · Provider: [DutchGreenhouses](/) Irrigation in a greenhouse is a closed chain rather than a supply line: source water is treated, dosed with fertiliser to a target EC and pH, delivered to each plant, then collected as drain, disinfected and returned to the supply. Sodium accumulation, not disinfection, sets how closed the loop stays. ## Facts | Property | Value | |---|---| | Drain fraction of dosed volume | 20–40 % | | How installation quality is actually measured | 2 measures | | Share of Dutch greenhouse area on substrate | 80 % | | Required removal of plant-protection actives before discharge | 95 % | | Legal minimum rainwater basin | 500 m³/ha | | Root-zone pH target band | 5.3–6 pH | Technology # Irrigation. Growing more with less water — and recycling what the crop returns. Greenhouse irrigation is far more than turning on a tap — it is a complete water-chemistry chain that begins with a raw water source and ends with the crop fed to the drop and the surplus reclaimed. Managed well, that chain lets a greenhouse grow more crop per litre than almost any other form of agriculture, cutting water use to a fraction of open-field farming while giving the grower precise control over exactly what each plant receives. The chain runs in stages, each depending on the one before. Source water — rain, well, surface or city water — is first pre-treated to make it crop-safe, correcting pH, removing particles and micro-organisms and softening hardness as needed. It is then enriched with a nutrient recipe and dosed, section by section, to the exact electrical conductivity and pH the crop requires at its current growth stage. The water the crop does not absorb drains away carrying unused nutrients and potential pathogens; rather than discard it, post-treatment disinfects that return flow so it can be safely recycled, and drainwater recycling blends it back into the supply — closing the loop toward near-zero discharge. Underpinning the whole chain is the growing method. Hydroponics replaces soil with inert substrate or pure water systems, turning the root zone into a fully managed environment with exact nutrition, ample oxygen and no soil-borne disease — the foundation of commercial greenhouse yields. And every link in the chain is monitored: EC, pH and volumes are logged per valve section and steered by the irrigation computer, so the grower can see precisely what the crop is getting and adjust with confidence. Because the right chain depends entirely on the source water quality and the local discharge regulations, irrigation is a genuine design decision rather than a commodity purchase. Explore each link below, or get in touch to have your water assessed and the system engineered around it. The chain ## From source to dripper and back. ### Pre-treatment Making source water crop-safe ### Fertilization Nutrient recipes per growth stage ### Dosing EC and pH, exact per dripper ### Post-treatment Disinfecting the return flow ### Drainwater Recycling Closing the water loop ### Hydroponics Growing without soil ## Water is a design decision. Source quality and regulations shape the system — we engineer the chain. Get in touch From the knowledge base ## Reads you might find interesting ceacultivationbusiness-case ### Grow Like a Pro: Starting Smart, Growing Strong How Grow Like a Pro combines smart farming, CEA technology and local partnerships for eco-friendly, profitable, pesticide-free greenhouse pr Read article education ### The Case for a College Greenhouse Why a college greenhouse belongs in the curriculum: teaching science, craftsmanship, business logic and sustainability, and preparing studen Read article education ### The Case for a High School Greenhouse Why every high school greenhouse matters: how it makes STEM tangible, builds responsibility and teamwork, and helps students discover their Read article education ### Greenhouses in Education: The Case for Schools Greenhouses in education reconnect students to reality — the full case for why every school, high school, college and trade program should h Read article historyconstruction ### The Origins of Greenhouse Horticulture: My Backyard A tour through greenhouse horticulture history: from 19th-century Westland fruit walls to the “City of Glass” and today’s international high Read article company ### DutchGreenhouses Rebranded: A New Corporate Identity Announcing our new corporate identity — a visual style reflecting our dedication to advanced, high-quality greenhouse projects and The Futur Read article ## FAQ **Is a recirculating greenhouse a closed system?** Not fully. Disinfection returns almost all drain water to the crop, but sodium is not taken up and concentrates with every pass until discharge becomes unavoidable. Leakage, drainage from soil-grown crops and crop-changeover cleaning water also leave the loop without passing any treatment step. **How much water returns as drain?** In substrate cultivation drain is 20 to 40 percent of the volume dosed, and that fraction is deliberate: it flushes salts out of the slab. Drain volume matters more than drain percentage — roughly 1 to 1.5 litres per square metre is needed to refresh a slab and correct its EC and pH. **How do you tell a good irrigation installation from a bad one?** By uniformity, not by the recipe. Two measures do it: the CU-value describes how evenly water arrives across the whole house, and the CV-value describes how far individual drippers deviate from their rating. A nutrient solution mixed to three decimal places and delivered unevenly produces an uneven crop, so the pipework and emitters decide whether accurate dosing means anything. **What must be treated before greenhouse water can be discharged?** Since 1 January 2018 Dutch growers must remove 95 percent of plant-protection actives from discharged water. The requirement is verified per substance against eleven reference actives rather than as an average across them, and imidacloprid carries a separate 99.5 percent requirement from its authorisation. **How does irrigation connect to greenhouse climate?** Directly. Transpiration is the crop's water demand and the greenhouse's main cooling mechanism at the same time, so an irrigation strategy and a humidity strategy describe one physical process from two sides. ## Related [Greenhouse Horticulture](/greenhouse-horticulture.md) · [Pre-treatment](/irrigation/pre-treatment.md) · [Fertilization](/irrigation/fertilization.md) · [Dosing](/irrigation/dosing.md) · [Post-Treatment](/irrigation/post-treatment.md) · [Drainwater Recycling](/irrigation/drainwater-recycling.md) · [Hydroponics](/irrigation/hydroponics.md) · [Humidity Control](/climate/humidity-control.md) · [Water Use & Circularity](/performance/water-use.md) · [Drip Irrigation](/glossary/drip-irrigation.md) · [Fertigation](/glossary/fertigation.md) · [Drain Water](/glossary/drain-water.md) · [CU-value (Coefficient of Uniformity)](/glossary/cu-value.md) · [CV-value (Coefficient of Variation)](/glossary/cv-value.md) · [Tomatoes](/vegetables/tomatoes.md)