Water Contain Hydrogen and Oxygen, and mobile phone motherboard which is also known as P.C.B (Printed Circuit Board ) contains Copper Track, various I.C (integrated Circuits) Electro Micro Components, Battery, Display and many more.
When Water collapse with mobile phone P.C.B it damage components, and in the presence of current, water starts making carbon which damage tracks of Electro micro components. as long as water present in P.C.B continuously it effects the Mobile Phone. that is why technician use to say that remove the battery first if your mobile phone got water damage.
Conclusion
So if your Phone got water Damage come to our service Center as soon as possible, we will do our best to repair your phone instantly.