What it is
This test lets the sample stand undisturbed for one hour, then measures the suspended solids in the water above whatever has settled. It is the companion to settleable solids: between them they split the total into the part that settles readily and the part that does not.
Where it comes from
Fine, light or colloidal material: emulsified fats and oils, fine food particles, biological floc, clays and silts, and anything held up by detergents. These are the solids that pass straight through a simple interceptor.
Why it matters
A high figure here, against a modest settleable-solids result, tells you that settlement alone will not get you inside your consent. Water companies sometimes write this specific determinand into consents for sites with settlement-based pre-treatment, to check it is doing its job.
What can be done about it
Fine solids need help to settle: coagulant and flocculant dosing, dissolved-air flotation, or filtration. Reducing detergent and emulsifier use in cleaning also lets fats and solids separate more readily. Pozzani can advise on dosing and treatment plant sized to your discharge.
Information last reviewed 6 October 2026 by Pozzani Pure Water.