# Pre-treatment > Part of: [Irrigation](/irrigation.md) · Provider: [DutchGreenhouses](/) Pre-treatment conditions incoming source water before it reaches the fertiliser unit. Rainwater needs little beyond filtration and storage; well and surface water carry iron, bicarbonate, sodium and pathogens that must be removed first, because every salt entering the loop concentrates with each pass and leaves only through discharge. ## Facts | Property | Value | |---|---| | Preferred intake water temperature | 15–20 °C | | Maximum iron for drip irrigation | 10 µmol/L | | Iron level above which de-ironing is advised | 0.6 mg/L | | Sodium in rainwater | 0.1–0.5 mmol/L | | Reverse osmosis recovery | 50 % | Irrigation # Pre-treatment. Every water source can be made crop-safe. ## Making any water source crop-safe, before it ever reaches the crop Pre-treating irrigation water is fundamental to a successful irrigation system. It is called “pre”-treatment because, chronologically, it is the step before fertilising — and because irrigation water comes into direct contact with a valuable crop, it needs to be controlled from start to finish. Continuously analysing the source water and anticipating its variation is what keeps a grower genuinely in control of the greenhouse. Four characteristics of the source water need to be managed, each with its own proven method, and in practice these technologies complement one another. The first is pH: controlling the pH of incoming water prevents algae and pathogens, particularly when water is stored in a tank or basin beforehand, and is handled in a shunt system that continuously circulates the water and doses acid or lye to hold a stable level. The second is micro-organisms, where there are two routes — UV treatment, in which pressurised water passes directly under UV lamps that kill organisms, and ultra-filtration, our system of choice, which removes them entirely so there are no residues left to feed new growth, with lower energy and maintenance costs than UV. The third is particles and sediment, most commonly filtered out with a maintenance-free paper-belt filter (flat-bed, deep-bed or hydrostatic, selected on capacity and contamination), where the filter paper sets the particle size removed. The fourth is water hardness, managed with a water softener to reduce chloride — installed before any tanks and systems, since hardness directly shortens the life of pumps, ducts and valves and makes fertilisation less efficient. For the most demanding inputs, reverse osmosis strips all micro-organisms, particles and minerals, giving a blank slate for precise (if costlier) fertilisation. Which chain you need depends entirely on the source. City (tap) water is the most stable and reliable, already treated and typically at ambient temperature, but it is the most expensive and can be high in chloride. Surface water varies in quality and quantity and demands more complex treatment; well water is often consistent and mineral-rich but must be tested regularly for contaminants; rainwater is an excellent source collected straight from the greenhouse roof, but its availability is inconsistent and needs a backup. Water temperature matters too: cold water holds more dissolved oxygen while warm water breeds micro-organisms, so the preferred choice is ambient water at 15–20°C, managed through a heat exchanger tied to the facility's heating or cooling system. A source-water analysis is always the starting point — the cleaner the input, the simpler the chain. Get in touch to have your water assessed. 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 **Why does source water quality matter more in a recirculating greenhouse?** Because nothing that enters the loop leaves it except through the crop or through discharge. Sodium in particular is barely taken up, so it concentrates roughly threefold per cycle as transpiration removes pure water. A source water carrying 3 mmol per litre of sodium forces discharge far sooner than rainwater at 0.2. **Which source water do Dutch greenhouses use?** Collected rainwater is the reference source because its sodium content is near zero. Well, surface and mains water are supplements when storage runs short. Dutch law requires at least 500 cubic metres of rainwater storage per hectare, though modelling shows that volume still forces mains water and discharge in a dry year. **Why is iron a problem for drip irrigation?** Ferrous iron oxidises on contact with air and precipitates as iron hydroxide inside pipes and emitters. Iron-oxidising bacteria accelerate it and bind the deposit into a slime, so the failure is chemical and biological at once. Drip systems tolerate under 10 micromoles per litre; overhead irrigation tolerates ten times more. **Is intake water treated the same way as returning drain water?** No, and the reason is that they carry different problems. Intake water is treated for salts, iron and bicarbonate, which are chemical loads that persist. Drain water is treated for plant pathogens, which is a biological load. Membrane filtration addresses the first; ultraviolet and heat address the second. ## Related [Irrigation](/irrigation.md) · [Fertilization](/irrigation/fertilization.md) · [Drainwater Recycling](/irrigation/drainwater-recycling.md) · [Reverse Osmosis (RO)](/glossary/reverse-osmosis.md) · [Rainwater Basin](/glossary/rainwater-basin.md) · [Drip Irrigation](/glossary/drip-irrigation.md)