When a mobile phone is damaged due to water i.e dropped in the water, got wet in the rain, etc., the phone will be switched off immediately. Don’t panic in that situation. Remove the battery (which is the power source) immediately. Shake the mobile to take out the water that went inside the phone. If you have hair drier, dry the mobile phone with low heat, mainly in keypad area (where water can enter into mobile phone easily), battery connector area, charging socket area, head phone socket area. Don’t blow the hot air of hair drier in one place of mobile phone continuously, which can damage the mobile phone body, and keypad mat which are mostly plastic and rubber made.
You also can use a small vacuum cleaner to dry up the mobile phone, but leave the phone for some hours in order to dry the moisture in the phone fully .
If you have the skill to open a mobile phone, do this drying process by opening the mobile phone, with which the phone circuit board area will be dried up without any moisture left.
If you feel that the mobile phone is dried up completely, insert the battery and check. In most of the cases the mobile phone switches on. If mobile phone is not switching on try with another similar battery or compatible battery, may be the battery voltage and current dropped to very low value due to the short circuit when the mobile phone is dropped in the water.
Why most of the mobile phones switch on again when the moisture is dried up?The technical reason behind this is that most of the mobile phones operate with very low current and voltage with which the electronic components inside the circuit board will not be damaged so easily. Also the intellectual software inside the mobile phone plays a good role.
If still the mobile phone is not switching on, contact a qualified mobile phone technician.