Diver can be detected by the air bubble they give off if NOT using a closed circuit rebrether. Additionally they can be detected with sonar as well as a hand held depth sonar type detector but at a limited range.
For your safety
dump the user and get a new best friend (if all else fails sell your house, get a scubadiving costume and buy a pineaple under the sea)
It is detected by seeing lots of water on the floor but it has to be more than 5 inches
It depends, using an average 12l tank (230 psi) if you are a heavy breather it will last for over an hour, and a light breather normally under 2 hours but you are recommended not to dive for over an hour
The neutrino.
When cobalt II chloride paper turns pink, this means that it has detected water. :-)
They are detected by chemical methods of analysis as spectrophotometry, ion specific electrodes, titrimetry, etc.
As strange as it may seem, yes water has been detected on the Sun. Actually what was detected is 'steam' over a particularly cool sunspot where the temperatures were only about 1000 K or so.....
because in earths Antarctica there is a layer of ice and under it there is water so that is why scientist hypnotise that
vital information resources under siege. it was the first Creeper to be detected on ARPANET.
Submarines will retreat to the depths if they are detected by radar. Note that radar can only detect a submarine if they are on the surface or if they have a mast or periscope sticking up out of the water. Radar has a terrible time trying to penetrate water, so if a submarine is detected because something is sticking up out of the water, the submarine will submerge to get some depth. Radar can't detect it down there. Also, the submarine will be trying to get out of the area and become "lost" in the ocean where it cannot be detected or located.
You can not drink enough.