Most residential water heaters will use an aluminum anode rod for their standard tanks. An aluminum anode rod is of the least expensive options and will last longer than most other anode rods. The AO Smith GCV-50-300 residential water heater has an aluminum anode rod with a steel core to protect against corrosion. The GCV has a 6 year warranty and is one of the most common water heaters installed by plumbing professionals. The same water heater is available in a 10 year warranty, the only difference in the tank is the anode rod used magnesium instead of aluminum. This is a bit surprising due to the fact the magnesium actually breaks down faster than aluminum. Without an anode rod the tank will rust out sooner.
If aluminum was consumed you would experience arthritis like symptoms and could upset your stomach.
A magnesium anode rod is slightly more expensive than other materials but can actually offer health benefits if consumed in drinking water. The downside to magnesium anode rods is that they dissolve much faster than other materials and may need to be replaced after 6 years.
Zinc anode rods are often mixed with aluminum or steel and are not as common today as in the past. The zinc can react with different metals to promote growth of bacteria. Many people that report a sour smell from their hot water have a zinc anode rod to blame. The anode rod can be replaced which should resolve the problem.
Water Softeners impact on an Anode Rod
A traditional salt water softener can break down an anode rod much faster than the normal rate. It is recommended that homes with a water softener replace the anode rod every 3 years to help protect the tank from corrosion.
Health Risks of Aluminum Anode Rods
The actual risk of using an aluminum anode rod is debatable. Wikipedia stats that under normal circumstances Aluminum is not water soluble and is well tolerated by both plants and animals. You should also consider that most of the time you will not drink from the hot water supply lines unless you have a circulating pump and a bad faucet cartridge that allows hot water to mix in with the cold.