Having hot water is important at all times of year, but it's especially important in the winter. If your water heater fails in the middle of winter, you really won't want an ice cold shower – and you may even have trouble with your pipes freezing. The best way to ensure you don't have to deal with these uncomfortable inconveniences is to inspect your hot water heater and make sure it's in good shape before winter hits.
Look at the bottom.
One of the most common problems that hot water heaters develop as they age is rusting at the bottom of the tank. Eventually the rust might work its way through the tank, causing a huge leak and forcing you to discontinue use of the heater. If you do see rust along the bottom of the water heater, have your plumber out to inspect it. They can tell you whether it's safe to try and get another year or two out of the appliance, or whether you need to replace it right now to avoid tragedy.
Inspect the in-flow and out-flow pipes.
Sometimes the problem is not so much the tank itself, but the plumbing connections to the tank. Look closely at the pipes leading in and out of the tank. If you see any drops of water around them, or if they are badly corroded, this is a bad sign, as it might lead to a leak in the cold winter months that follow. You can try taking some vice grips and tightening the pipe connections. Wrapping some plumber's tape around the connections may work, too. If the drips persist in spite of these fixes, you'll need to have you plumber out to replace or more effectively repair these pipes.
If your hot water heater is not well insulated, it will have to work harder in the winter to keep water warm. The harder it works, the more wear it will experience, and the greater the chances of failure. Read your water heater's label to determine if it is a self-insulate unit. (Many newer ones are, but most old models are not.) If it's un-insulated or if you're not sure, purchase a water heater "blanket" at a home goods store. This is a big, insulated sleeve you can slip over your water heater to reduce heat loss and its work load.
If there's any doubt that your water heater will survive the winter, replace it now rather than risking a few days without hot water.