Water Dye is a tube of liquid dye which can be used to highlight a patch of water (around a raft at sea, or in a lake near a crash site) with a bright, easily spotted color visible from the air.
The primary drawbacks to this form of signaling are the short duration of the colored patch (it lasts no more than 15 minutes in stall water, much less if water is rough or there is any form of precipitation to break it up). and the fact that it can not be used at night. The latter problem is offset in dyes available at TL–9, for twice the basic cost. These contain a phosphorescent dye equally visible in day or night.
Generally, water dyes are useful only when searches are aware of the presence of the distressed travellers, and are in need of an exact location than some signal to draw their attention in the first place. A tube provides a single dye patch of around 10 meters diameter.