What it is
Phosphate is the form of phosphorus that plants take up. In water it comes from minerals, fertilisers and detergents, and public suppliers add a little to protect pipework. It is reported for hydroponic growers because it affects how much phosphorus the nutrient solution needs.
Where it comes from
Natural phosphate comes from phosphate-bearing rocks. Agricultural run-off, sewage effluent and detergents raise it, and treated mains water usually contains a small dose added to reduce lead and copper pick-up.
Why it matters
There is no drinking-water limit and phosphate is not a health concern. In open water it drives algal growth. For hydroponics the point is simply to know the starting level so the feed recipe can allow for it.
What can be done about it
Growers usually adjust the nutrient recipe rather than treat the water. Where a very low or controlled baseline is wanted, reverse osmosis gives a clean starting point.
Information last reviewed 5 October 2026 by Pozzani Pure Water.