Hot water heater drip pan?

no its not normal fer a water heater to have any water in the drip pan. you say it happens after you use water? it could be the presser re leaf valve spring getting tired and letting out a small amount when you stop using water that's when the water is most likely to squeeze out. or worst case an element can leek on electric models. last thing if its gas look in the bottom ware the flame is, if you see water chances are your tank has a hole and will need replacing.

Look on the side of the water heater at the top and you will find a brass fitting with a little handle on it. There is usually a straight piece of 3/4" copper pipe screwed into the bottom of it leading into the water heater pan. Put your finger at the bottom of the pipe, if you feel water in the pipe the Temperature and Pressure valve needs replacement. I have put a link to a replacement at Home Depot below. If the pipe end is dry the next thing for you to check is where the two pipes are attached at the top of the heater. Look carefully with a flashlight to see if water is accumulating in the dimple the pipes sit in. Sometimes the nipple at the top of the heater that the incoming cold pipe and outgoing hot pipe are attached to are weeping water. It would then trickle down behind the steel outer skin of the water heater. If you don't find water at either one of these locations you will need a new water heater probably. You can usually find a date of manufacture somewhere on a nomenclature plate, and if it is older than 10 years you would be better off with a new one anyway because of the efficiency of new heaters. I usually write the date of install with a Sharpie when I replace water heaters. The T+P valve would require you to turn the cold water off, bleed off a few gallons out of the heater with a hose, unscrew the copper pipe, then the old T+P valve, then reinstall the new one with pipe dope or teflon tape: same with copper pipe and you are done. If the nipples are leaking you might need a plumber to replace them.

Look on the side of the water heater at the top and you will find a brass fitting with a little handle on it. There is usually a straight piece of 3/4" copper pipe screwed into the bottom of it leading into the water heater pan. Put your finger at the bottom of the pipe, if you feel water in the pipe the Temperature and Pressure valve needs replacement. I have put a link to a replacement at Home Depot below. If the pipe end is dry the next thing for you to check is where the two pipes are attached at the top of the heater. Look carefully with a flashlight to see if water is accumulating in the dimple the pipes sit in. Sometimes the nipple at the top of the heater that the incoming cold pipe and outgoing hot pipe are attached to are weeping water. It would then trickle down behind the steel outer skin of the water heater. If you don't find water at either one of these locations you will need a new water heater probably. You can usually find a date of manufacture somewhere on a nomenclature plate, and if it is older than 10 years you would be better off with a new one anyway because of the efficiency of new heaters. I usually write the date of install with a Sharpie when I replace water heaters. The T+P valve would require you to turn the cold water off, bleed off a few gallons out of the heater with a hose, unscrew the copper pipe, then the old T+P valve, then reinstall the new one with pipe dope or teflon tape: same with copper pipe and you are done. If the nipples are leaking you might need a plumber to replace them.