Replace it, repair it, or ignore it? All building systems have a lifespan, or lifecycle based on average usage and regular maintenance. Water heaters are no different. Most water heaters have a lifespan of about ten years. Of course, average use allows for variance.
One of the most common variables is how much water do you use. Volume of use effects the water heater in two primary ways. If you use a lot of hot water, you have to heat a lot of hot water. That means your heating element is going to get extra use. Also, water is corrosive. More water equals more corrosion.
Not all water heaters are manufactured equally. Studies confirm that more expensive water heaters, with longer warranties (9-12 years) truly are built better. You will see things like higher-wattage heating elements (heat more water faster ultimately means less use), thicker insulation (heat the water less often). You may also find features like rust protection porcelain lining. Have these systems professional installed and repaired. If repairs are needed, consider replaced if costs will exceed 10% of the cost of the unit or will required voiding the warranty.