Here is how you check:Liquid Indicators are installed inside the iPhone. DO NOT disassemble your iPhone as you can incur significant irreparable damage.
Look in your HEADPHONE JACK. The very back of the hole will be white or silver. If the back of the hole is RED then the iPhone has water damage.
Look in your CHARGING DOCK. If you look in the charging dock hole towards the bottom you will see something white. If you see a RED color then the iPhone has water damage.