I cleaned out the utility closet and noticed that one of the water heaters is sitting in a tray of standing water. It smells nasty. Is this standard?

I'm renting and the house is extremely old and in poor condition. I never open this closet, but today I had to change the furnace filters.

I know those random moldy panels against the wall need to go. I e-mailed my property manager about what to do with them since my dumpster is too small to fit them. I also let her know I'm concerned about the water heater.

Thank you in advance.