If you have a floor drain near buy you could temporarily divert the water to the floor drain until you can fix the faulty drain valve.
If you don’t have a floor drain or a sump pump to temporarily run the dripping drain valve too, you could try to put a cap on the valve. This could be a remedy for a long time and give you enough time until you can afford to fix the valve or replace the water heater.
If you decide not to make repairs to the faulty valve and decide to replace your water heater you will probably need to pull a permit. Check with local state & city building department.
Turn the gas valve off, and then turn the control box to the off position.
The gas valve in this picture is the yellow handled valve on the right.
The gas control valve. Shut off
Turn the water valve off. (see picture above).
Many homes will not have a valve to shut the water off so easily. You may have to turn the water off in the crawl space or in the basement. If this all fails than you’ll have to turn the water off near the side walk where the city reads your meter in the pit. Turn all the water faucets on to drain the water faster and open the drain valve if you can.
Try your crescent wrench first and see if you can unscrew the drain valve counterclockwise to loosen it. If the crescent slips, than use your pipe wrench. Remember the bigger the wrench the easier it is to remove, but you need to have enough room to move the wrench.
Be gentle and take the valve out slowly to insure there is not a build up of pressure and you don’t get hurt or all wet. The valve that you see in this picture is around 6 inches long total including the nipple it is attached to.. When you replace it with a new brass nipple and boiler drain valve insure you get close to the same length.
Install the new valve and nipple insure you use either Teflon tape or paste on the threads only.
The picture above is a boiler drain valve. You can use this style or something like it to replace the existing valve to make your repairs.
Turn the water back on and slowly start turning the faucets back off. Insure you have no air left in the lines and turn the gas on and relight the pilot.