What to do when your Mobile got wet due to fall in water and not working?

It might be a bit late now to answer this but still, for the information of others, here are the things you can try-
1. Immediately remove the battery if it has removable battery and Do Not try to switch it on. You might cause a short circuit damaging the motherboard permanently.
2. Keep your smartphone on a mildly hot and dry surface like a stabilizer after drying it as much as you can do with a soft cloth. You can also keep it in a container with some moisture absorbing material like rice.
3. Once it is dried, use a hair dryer or something similar to remove last traces of moisture and try to switch it on.

Since most smartphones nowadays come with in built battery, there is very less chance to prevent a short circuit. If you have the same type of phone, I doubt it would work now. Warranty does not cover physical damage or damage due to moisture.

It's not possible to have your phone working again.
I am providing precautions below, these are the steps you need to follow after your cell phone falls into the water.
1) Take it out of the liquid immediately. Clear water causes less damage.
2) Turn it off as early as possible.
3) If the power stays on the phone runs the risk of short-circuiting.
4) If the power button is not working, take out its battery. If the phone is already off, leave it switched off.
5) Remove the battery
6) Do not plug your phone in while it's wet
7) Remove the SIM card, memory card, and all its peripherals.
8) Dry the phone with a cloth or microfiber towel.
9) Don't use an oven, microwave or hairdryer.
10) Gently shake your phone dry
11) Put the phone in a vacuum bag.
12) Store your phone in a safe dry place.
13) Give your phone at least 2 days to dry
14) Check if you have your warranty through a third party vendor such as Asurion or Squaretrade.
15) Turn it on, and cross your fingers.

Best way to recover a mobile phone after it has fallen in the water is to use an air blower to dry the mobile from inside. The water that enters in the mobile, deposits salt and dirt on the circuit board and blocks the route causing a few commands/all commands to not work properly. Sometimes, the mobile may not be switched ON due to this. Input is going but it is not getting processed due to the moisture present inside the mobile. So, our first step is to dry the mobile from inside and the best way to do this is by using an air blower. Remove the battery if possible. Do not connect the charger until the moisture/ water is completely out of the mobile. Place the mobile outside on the roof or on a wall against sun light. If you think that the mobile is completely dry by using above tips now you can switch it on and your mobile will work perfectly good.

In fact, the best option to take care of your phone after it has taken a water bath would be to check if the battery can be removed. With a large number of phones these days coming with a non-removable battery, it may be an impossible task. Switch off your phone immediately. Leave it switched off and don't try switching it on.
Remove SIM card, memory card and other accessories to prevent damage to them.

Try drying out your phone to the maximum extent. A few experts suggest submerging it completely in a highly absorbent material like rice.