Fluorescein dye test for leaks
Fluorescein is a non-toxic, fluorescent green dye that is visible at very low concentrations, especially under a UV lamp. We dye the water from one appliance or one specific area, then watch where it reappears: if the dyed water shows up in the damp patch, we know where the leak is coming from.
How it works
The test is done one source at a time: the shower drain, the basin, the WC, a terrace outlet, an upstand in the waterproofing. The dyed water is run in one place only, and the damaged area is watched. When the colour appears, the source has been found.
When we use it
- drains: which appliance or which joint is at fault;
- showers and baths: the waste or the waterproofing;
- water ingress through a terrace, a balcony or a flat roof, by targeted flood testing;
- checking a connection: is an appliance actually connected to the sewer?
Limits
Fluorescein identifies the source, not the exact point of the leak along the way. It also requires the water to reappear visibly: if it soaks away into the ground, nothing can be seen, and we move on to a CCTV drain survey or a smoke test.
Frequently asked questions
Is fluorescein harmful?
No. It is used at very low concentrations and is also used to trace groundwater, precisely because it is safe for the environment at these doses.
Related pages
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