Unless your well water pressure tank leaks from a plumbing fitting, such as the water supply line, fixing a well water tank is near impossible, as it is a sealed, welded and self-contained unit. When you find that your well water pressure tank leaks, hunt down the source to determine whether you can fix it. While leaks do happen in a pressure tank other than the area around the fittings, for the most part a leak in the tank's seam or construction is the exception rather than the rule.
Pipe Fitting Leaks
Establish the point of the leak on the well water pressure tank. Use a dry towel and wipe the water from the tank and pay attention to where the water emerges. This may require some sleuthing as plumbing leaks usually have a point of origination away from where you find the water pooling.
Turn off the circuit breaker that powers the well pump and the pressure switch after determining that the leak comes from a pipe fitting. Drain the tank of water after shutting off the power supply to the pump and switch.
Detach the water line fitting using the pipe wrench and clean the threads around the male water pipe. Inspect the fitting for breaks or cracks, as it is not uncommon for these to occur over time, especially if the pipe is exposed to the weather.
Replace any needed pipe sections by cutting the PVC pipe and adding a female coupler to the pipe from the well. Use a hacksaw or reciprocating saw and remove the bad pipe section. File the end of the cut section to remove any burrs and follow up with a buff of the sandpaper. Swab the inside of the female coupler with the purple pipe primer followed by the glue. Hold the coupler on the pipe from the well for about a minute. Swab the end of the female coupler with primer and then glue and do the same for the non-threaded end of the pipe that will attach to the pressure tank. Hold in place for a minute. Wrap new plumber's tape around the threaded male end and secure to the pressure tank using the pipe wrench.
Turn the circuit breaker back on and allow the tank to fill with water. Check the fitting to confirm it is no longer leaking.
Test The Pressure Tank
Turn off the power to the pump and pressure switch. Open the nearest valve to drain the water pressure tank. Carefully nudge the pressure tank without detaching the water line and listen for the sound of sloshing inside. If you hear sloshing, this is one indication that the tank may have a broken water bladder. This requires complete replacement of the pressure tank as it cannot be fixed. If it doesn't slosh, move onto the next step.
Test the air pressure in the tank to see if it is set too high, forcing the tank to leak at its fittings. Complete this test while the tank is still empty. Place the tire gauge onto the air fill valve and note the pressure setting. The tank should contain 2 pounds per square inch less pressure than the pressure switch's cut-in setting for the well pump. When the pressure switch is set to turn the pump on at 30 psi, the pressure tank should contain no more than 28 psi.
Remove excess much air in the tank to adjust its pressure. Use a screwdriver to push in the small stem inside the air fill valve to release the extra air. Test the air pressure with the tire gauge again and add or release air until it is at the right pressure.