What it is
Molybdenum is a trace element that plants need to convert nitrate into protein. Deficiency and excess both affect growth, so growers want to know the level in their incoming water.
Where it comes from
Molybdenum dissolves from natural minerals, particularly in some shales and mineralised areas, and is raised by mining and industrial activity. UK water levels are usually very low.
Why it matters
There is no UK drinking-water limit; the World Health Organization considers a health-based value unnecessary at the levels normally found. For hydroponics the result is used to set the feed.
What can be done about it
Growers normally adjust the nutrient solution to the measured level. Reverse osmosis provides a low, consistent baseline where that is preferred.
Information last reviewed 5 October 2026 by Pozzani Pure Water.