What it is
Silica is dissolved silicon dioxide, the same material as sand and quartz. Most groundwater contains some. Plants take up silicon and many growers regard it as beneficial, but it also forms hard, glassy scale on equipment.
Where it comes from
Silica comes from the rocks and sands the water passes through; levels are higher in groundwater from sandstone and volcanic areas than from chalk.
Why it matters
There is no drinking-water limit for silica and it is not a health concern. For hydroponics it is part of the nutrient picture, and high levels can scale heaters, pumps and misting nozzles.
What can be done about it
Silica is one of the harder things to remove from water. Reverse osmosis takes out most of it; specialist ion exchange removes more where equipment demands very low silica. Many growers simply allow for it in the feed.
Information last reviewed 5 October 2026 by Pozzani Pure Water.