Accidents happen with phones and water but it doesn't always mean that all hope is lost. Below is a brief guide as to what you should do if your phone has been totally immersed in water.
1. Take the phone out of the water as quickly as possible.
2. Do not attempt to switch it on as this may cause further damage.
3. Remove the battery as quickly as you can, also remove the memory and sim cards.
4. If dropped in fresh water dry it off with a towel. If dropped in salt water rinse it thoroughly with fresh water. I know it sounds crazy getting it wet again but salt can cause a lot of internal damage such as corrosion. Again dry with a towel. You may also want to rinse it if you dropped it in a toilet.
5. Place the phone, battery and it's wet accessories in a plastic container (like a lunch box) and completely cover it with uncooked rice, use plenty of it. Again this sounds crazy but rice has desiccating properties that help draw the water out of the phone. Do not place a lid on the container.
6. Place the container somewhere very warm and dry for at least 3 days. An airing cupboard is often the ideal place.
7. Do not use a hair dryer directly on the phone to speed up the process. Too much heat can cause even more damage.
This isn't guaranteed to work but many people have successfully revived their phones and retrieved their data using this method.
Keep in mind that your phone is on borrowed time after you do this. Make it your first priority to retrieve any data that you would like to keep. It may only work for a few minutes, days, weeks, months or it may even last years.
You should monitor the phone carefully during charging. If it gets very hot the battery may be damaged and should be replaced.
After any exposure to water you no longer have a warranty as water damage is not covered. Any insurance policies on the phone may also be voided unless you are covered for accidental damage.
A more efficient alternative to rice is silica gel. You most likely won't have enough of the stuff to hand when the accident happens but it is good to use. Silica gel can be bought from electronic wholesalers like this example
. Thank you to shuntfield for this information.