Hot water heaters constitute one of the worst chronic water leaks in many houses. The question is not if a water heater will leak but when it will leak. They will all eventually leak and the leak may be so small it goes undetected for long periods of time. All water heaters should be placed in a pan which is plumbed to the sewer or have a drain built into the slab underneath them. This will allow most leaks to not cause a mold problem during the early stage. Placement directly on the floor is just asking for a problem.
