I've got an R&D test I'm working on for my day job and I've run into a snag.

Essentially the problem is that we have some water collecting gutters of a unique profile but we don't have a way of detecting exactly how much water is flowing out of the end of the gutter system. The gutters are made of a PVC extrusion and are dark grey. Filming them dead on isn't going to work as they are part of an enclosed compartment with hurricane force water being sprayed directly down.

The idea we've come up with is to paint the inside surfaces of the gutters near the open end with a water soluble paint which will be removed by the flowing water, but not by any spray.

Does anyone know of a product like this?

We've tried dry-erase markers, finger paint, chalk and a powder film. The water doesn't seem to remove any of these.

__________________
Onus probandi incumbit ei qui dicit, non ei qui negat

I recondition w123/w126/w124/w140/r107/r129/ steering boxes!


1984 300D "Elsa" odo reset 6/2011 147k
1983 300TD "Mitzi" ~268k OM603 powered
1995 E300 "Adelheid" 262k [Sold]