On Sun, 30 Oct 2016 12:06:38 -0400, Ed Pawlowski wrote:

On 10/30/2016 10:44 AM, wendy vonlienen wrote:
am putting new floor under gas hot water heater,there is a hole in old
floor
under water heater for vent i think?can i cover it up


That vent may be very important. It may be the source of air for
combustion.

The OP never mentioned the type of water heater. If it's gas, it may
need the combustion air. If electric, it's NOT needed for combustion.
However, all water heaters need some sort of drain in case of a leak.
Normally, if it's a drain, buy a plastic or metal base. (Pan under the
heater). Those drain outside with a piece of pipe.