PCB s' can be coated with Transparent Epoxy so that water vapour (due humid whether) particle will not make effect the circuit.
Like under water camera case..need to design and test..some sensitive to pressure and temperature..
Go on the web to Integrated Surface Technologies. They have a nano-meter thick depositing technique that produces water-proof electronics. Like cell phones you can drop in the toilet. Have a look.
_The_ classic method for short-term proofing is to stuff (ok, not really - these things can rip fast) the device into a condom and make a knot on the end. Try to find one that uses as little (and as non-aggressive) lubrication as possible, that trick stems from a time when condoms were not customarily lubricated with a spermicide.
Depends on exactly what you mean by "water proof". Polymers have a characteristic "MVTR" (moisture vapor transport rate" so even sealing it inside a "plastic bag" does not mean it will be perfectly dry forever. If you need a "hermetic seal", you need to get really specific about the range of conditions you expect it to see. This is science so, if you want a specific answer, you need to ask specific questions.
"encapsulate" it in RTV rubber.
You by RTV Rubber by the tube at any hardware store -- Ace, Lowes, Builders Square, etc.
put your phone in a zip lock plastic bag (the one you can seal up and open again)
Conformal coating is what you are looking for
I'm not going to submerge the device in water or anything, its just going to be in an environment where significant amount of water condensation occurs,
