Every once in a while during a home inspection, a client will ask, "Why does the water heater make that gurgling noise?" The reason is that the water heater is heating the sediment that has collected in the tank.
The water in South Texas is very hard, due to the high limestone content in the soil. The sediment separates from the water and falls to the bottom of the tank, building up on the tank and the heating element or boiler plate. The heating element must work longer to heat the water, because the sediment absorbs the heat. The US Department of Energy (DOE) reports that as little as a 1/32 inch scale build-up on a hot water heater causes you to use almost 10% more energy. A 1/4 inch build-up will increase energy consumption by as much as 40%! This can cost hundreds or even thousands of wasted energy dollars per year. It also causes the unit to wear out sooner.
If your water heater is making gurgling noises:
Drain the tank and flush it out
Remove the heating elements, soak them in vinegar, then scrape off the mineral scale
Heating Elements with Mineral Scale Build-Up
An Ounce of Prevention
Draining the water heater tank a couple of times a year will get rid of the sediment before it has a chance to build up, causing the water to heat faster and more efficiently, and increasing the lifespan of the water heater.