Dropped mobile in water

Unsure from your question whether your phone was water damaged recently or a year ago.

If it was recent, take out the battery and place the phone inside a packet of uncooked dried rice. The rice with help pull any moisture from the phone and aid it drying out. Keep it in the rice for a few days.

If you dropped your phone in water last year and you find your battery is no longer lasting how it should then there is a chance the battery is failing, telltale signs would be the fattening or swelling of the battery as the water Ingressed at the time of submersion mixes with the internal lithium structure of the battery making it expand from the inside. If this is the case then the battery is certainly going to need replacing as the chemistry of the battery has been diluted by the water, meaning the battery efficiency will be declining.

Hopefully it's not an iPhone, as you cannot access or change out the battery without dismantling the unit and can be tricky for novices.