A wet ring on the garage floor is easy to step around the first time. By the second or third time it is worth kneeling down with a flashlight, because water sitting at the base of a tank is rarely where the trouble starts. It is just where gravity put it.
Reading the puddle before you touch anything
Everett homes push a lot of hot water through hard-working tanks, and most of what ends up on the floor traces back to one of four places: the cold and hot connections at the top, the temperature and pressure relief valve on the side, the drain valve down near the floor, or the shell of the tank itself. The first three are fixable in an afternoon. The last one is not fixable at all.
Start by drying everything with a towel and laying a sheet of cardboard or newspaper under the unit. Come back in an hour or two. Where the paper darkens first tells you more than any amount of squinting at a damp slab, and it separates a slow weep from condensation, which is common in unheated Snohomish County garages during a cold snap and disappears once the room warms up.
Other signals are worth noting while you wait. Hot water that fades sooner than it used to, a low rumble or hiss while the burner runs, or a rust stain running down the jacket below a fitting all point in different directions. Rumbling usually means sediment on the tank floor, which is a flushing problem. A stain below a union usually means a fitting that needs a wrench, not a new heater. If the trail is not obvious, it helps to narrow down where the water is actually coming from before you start taking anything apart.
The repairs a homeowner can reasonably take on
Before any of this, cut the energy supply. On an electric unit that means the breaker, not the thermostat. On a gas unit, turn the control knob to off and close the gas shutoff. Then close the cold water inlet valve at the top of the tank and open a hot tap somewhere in the house to drop the pressure.
A weeping drain valve is the most common small failure. The plastic ones that come on budget tanks tend to seep after a few flushes once grit gets into the seat. A brass replacement, threaded in with fresh tape or dope, usually ends it. Loose unions at the top are next most common: a quarter turn with a wrench on each side of a dielectric nipple is often all a slow drip there needs, and overtightening is a real risk on older galvanized fittings.
The relief valve deserves its own paragraph. If it is dripping, it may be doing exactly what it was built to do, which means the real issue is pressure or temperature in the system rather than the valve. Turning the thermostat down a notch and checking the expansion tank is the right order of operations. Never cap or plug the discharge tube to stop the drip.
Then there is the leak that is not a repair. Water seeping from the vertical seam, or appearing from under the jacket insulation with no wet fitting above it, means the steel tank has corroded through from the inside. No sealant, epoxy or clamp holds against that for long, and the failure gets worse rather than better. At that point whether a patch is worth it or the tank has reached the end is the question worth settling before anyone spends money on parts.
Keeping the next one further away
Draining a few gallons off the bottom once a year keeps sediment from building into a layer that insulates the burner from the water above it. It is a ten-minute job with a garden hose and a bucket, and it is the single maintenance habit that most affects how long a tank lasts here.
The anode rod is the other piece worth remembering. It is a sacrificial length of metal that corrodes so the tank does not, and once it is spent the tank starts taking the damage instead. Pulling it for a look every few years, and replacing it when it has worn down to wire, is far cheaper than what follows if it is ignored. While you are there, glance at the expansion tank and the shutoff valves, both of which tend to be forgotten until they are needed.
Keep the floor around the base clear and dry so the next drip is visible the week it starts rather than the month it starts. If the heater sits above finished space, a drain pan plumbed to a drain line is worth the small cost. And if the tank is well into its second decade and the repairs are starting to stack up, planning a replacement on your own schedule is an easier thing to live with than handling it the morning it lets go.
One last thing that catches people mid-flush: all that water has to go somewhere. If the laundry sink or the floor drain backs up while you are draining the tank, the heater is not the problem, the drain line is, and that is a different trade from the one that works on the heater. For the drain and sewer side of the house, everettdraincleaning.com is a good place to start.