The honest answer is: it depends enormously — on the crop, the season, the glasshouse itself and, above all, how the irrigation system is designed. Two glasshouses of identical size can have completely different water demands, and any generic figure you find online will be wrong for at least one of them. What’s genuinely useful is understanding what drives the number for your site, because that’s what decides how your supply, storage and pumps should be sized.
What actually drives glasshouse water demand
- The crop, and its stage. A bench of young plants and a bench of mature, fruiting crop use very different amounts of water for the same footprint. Tomatoes, cucumbers and peppers each have their own demand curve through the growing cycle.
- Open vs closed system design. This is the single biggest lever. An open irrigation system loses everything that drains past the root zone; a closed, recirculating system captures and reuses that drainage. The difference in total water use between the two can be several-fold — same crop, same glasshouse, radically different demand on your supply.
- Season and climate. A hot, bright July day can demand several times the water of a dull February one, even on the same bench. Annual averages are almost meaningless for design purposes.
- Glasshouse design and age. Ventilation, shading and glazing all affect how much the crop transpires — and therefore how much water needs replacing.
Why peak demand matters more than the average
Water demand isn’t flat across the year — it peaks hard in summer and drops right off in winter. It’s the peak-day figure, not the average, that decides whether your water storage is big enough, whether your pump can hold pressure when every zone is calling for water, and whether your abstraction crosses the Environment Agency’s daily licensing threshold. We cover that threshold, and how to plan around it, in our guide to water sourcing for irrigation.
Size a system on the average and it falls short exactly when the crop can least afford it. Size it on a generic industry figure and you either overspend on capacity you never use, or under-build and spend every summer fire-fighting.
Every glasshouse needs its own number
This is why we don’t publish typical consumption figures: every job is different, with different crops, different components and different constraints. The right way to get your number is a proper site assessment — your crop plan, your system type, your glasshouse and your water source, worked through together. That calculation then sizes everything downstream: storage, pumps, fertigation and controls.
Want the answer for your glasshouse?
We work out actual peak-day demand for your crop, your glasshouse and your system as part of a design visit — no generic assumptions. Get in touch to arrange one.