Food colouring

[Pickled Onion]

There was a substantial amount of water in the bilges of my boat this week. I've no idea how long it took to get there as I've not looked under the floor until now and it looks fairly clean so first suspicion is it might be from the fresh water tank - the level went down quite quickly last time I filled it. The previous owner says the bilges were generally dry except when the shower drain leaked.

Would it be a bad idea to dump a bottle of red food colouring into the tank to see if it ends up in the bilges?

[Kim]

You can get fluorescein powder for this sort of thing.  Probably cheaper than food colouring, and more visible at low concentrations.

[neilrj]

Can you flush it easily if whatever dye you use doesn't actually get to the outside? Basically don't go mad with any dye if it's a bigger to flush...

[Pickled Onion]

You can get fluorescein powder for this sort of thing.  Probably cheaper than food colouring, and more visible at low concentrations.

Is that safe for a potable tank? It sounds like it's more for drains and swimming pools. Hence the first thought being food dye, as after a simple flush through I imagine it won't do me any harm.

[L CC]

It might stain though?

[hellymedic]

Fluoroscein is injected for some medical imaging.
It is used in eye drops to detect corneal abrasions and check contact lens fit.
They use it in fizzy Vitamin C tablets.
It gives you day-glo urine but it's pretty safe...