During secondary school Chemistry lessons decades ago, I learnt about some metals acting as sacrificial sources to protect another metal against rusting. This nugget of information was stored away in my head (even after my O Levels exams!) and I thought I would not see it in action in my daily life.

According to Google, sacrificial anodes are highly reactive metals (such as zinc, aluminum, or magnesium) attached to less reactive, critical structures. Through galvanic corrosion, the sacrificial anode intentionally corrodes first, absorbing damage and protecting the more valuable metal underneath from degrading.

Common Materials & Applications

• Zinc: Best for saltwater environments. Commonly used for recreational boat hulls, outboard motors, and sterndrives.
• Aluminum: Highly effective in both saltwater and brackish water, often used on larger marine vessels and commercial ships.
• Magnesium: Has the highest electrical potential and is typically used in freshwater environments or for buried infrastructure, such as underground pipelines and home water heaters.

With the cold weather in Melbourne, hot water for showers and cooking is usually heated up by gas or electricity and stored in outdoor storage tanks.

Melbourne water is generally “soft” with less dissolved salts (compared to “hard” water with more dissolved minerals).

The outdoor hot water tank will have a long rod made primarily of aluminium acting as a sacrificial node to ensure that over time, this replaceable rod rusts, instead of the metal body of the tank. Such sacrificial rods normally lasts for 10 years or so.

My hot water tank is up on the roof so it wasn’t that easy to determine for myself if my hot water system is still in good condition. I decided to bite the bullet to pay for a plumber to come inspect the entire system and to replace parts where necessary.

It turned out to be a good decision.

The plumber showed up and proceeded to first check the all important sacrificial rod. It looked like a giant rusty toothpick. Not much service life left!

He also checked the electric heater coil (yes, rusty too) and the various valves.

At the end of the inspection, I had to replace the sacrificial rod, the tank thermostat, the heater coil and the tempering valve as well.

With that, my system is good for another 5 to 10 years till the next maintenance inspection.

I would recommend the above checks to be done for your hot water system, especially if you have no idea when the last time someone looked it over.

No fun being caught out without hot water in winter!