How does a water heater's anode rod work and why does it need replacing?

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1. 1

   CATHODIC PROTECTION FEASIBILITY OF WATER HEATERS

   Corrosion & Protection (Huang)Published Jan 1, 2006Checked Oct 17, 2026

   “The corrosion mechanism and electrochemical performance of water heater inner hull were studied experimentally alloy and the protection method was optimized.Magnesium sacrificial anode was usually adopted to protect the inner hull of water heaters.The disadvantage of this method was that the potential difference between magnesium anode and inner hull was too big.The consuming of anode was quick so that the anode life was less than 2 years.Impressed current cathodic protection method is a perfect method used in water heater.A noble metal is adopted as the auxiliary anode and cathode is the water heater inner hull.The system adopts constant voltage controlling method,it is easy and convenient.The anode will not be dissolved and has long life,so the water heater can be used for long time.”

2. 2

   Cathodic Protection of Hot Water Tanks at Fort Sill

   US Army Corps of Engineers: Engineer Research and Development Center (Knowledge Core) (Stephenson et al.)Published Jun 1, 2007Checked Oct 17, 2026

   “The cathodic protection systems were designed to provide corrosion protection to the bare steel interior of the tanks that are susceptible to corrosion. This is a first time installation of horizontal anode in large hot water storage tank ASME Pressure Vessel with no man-ways. These cathodic protection systems have continued to operate as designed since their initial operation in April 2006 and have provided complete corrosion control since their original installation. The lifetimes of these large tanks are expected to be extended 30 years as a result of installing the ICCP systems using ceramic coated (mixed metal oxide) anodes. In addition, 17 smaller hot water tanks and hot water heaters (37 to 1,000 gal) were replaced with new hot water tanks and hot water heaters with factory-installed sacrificial anodes and glass linings. For the smaller tanks, it is more economical to use glass linings and sacrificial anodes than ICCP systems.”

3. 3

   Reducing Corrosion Rate for Electric Water Heater in Welding Joints by Using Sacrificial Anodes

   Iraqi Journal of Industrial Research (Kassim et al.)Published Dec 14, 2025Checked Oct 17, 2026

   “Consequently, electrochemical reactions are initiated, involving the flow of electrons from the anodic to the cathodic regions in the presence of a conductive medium (water), thereby accelerating the corrosion process in the welded zones. In this research, a linear polarization system (Potentiostat MLab-200) was employed to measure the corrosion current density (Icorr) and corrosion potential (Ecorr), followed by the calculation of corrosion rates at various temperatures 30, 40, 50, 60, and 70°C under conditions simulating the actual operation of an electric water heater. The results indicated that the corrosion rate of galvanized iron prior to welding was approximately 2.0 mpy at 70 °C, whereas it increased to 3.0 mpy after welding at the same temperature. To mitigate this corrosion, a sacrificial zinc anode was introduced into the heater system, which reduced the corrosion rate to 1.9 mpy at 70°C. This implementation contributed to prolonging the service life of the heater and enhancing its operational efficiency.”

4. 4

   Evaluation of the Corrosion of AZ31 Magnesium Alloy Used as Sacrificial Anode for Cathodic Protection of Hot-Water Tank Storage Containing Chloride

   International Journal of Electrochemical Science (Zidane et al.)Published Dec 16, 2017Checked Oct 17, 2026

   “Corrosion resistance of AZ31 magnesium alloy was evaluated in aqueous chloride-containing solutions. Combined weight loss and electrochemical data indicate that corrosion rate of magnesium alloy increased for greater NaCl concentrations and higher temperatures. Corrosion is characterized by the formation of precipitates, that present the distinctive XRD patterns corresponding to crystalline phases of Mg(OH) 2 , accompanied by H 2 evolution, these processes leading to pH increases in the solution. Retrieved samples show a film of corrosion products distributed around cracks on the bare metal surface, and the subsequent development of large pits that prevent the material from attaining passive protection.”

5. 5

   Shotgun Metagenomics Reveals Impacts of Copper and Water Heater Anodes on Pathogens and Microbiomes in Hot Water Plumbing Systems

   Environmental Science & Technology (Song et al.)Published Aug 29, 2023Checked Oct 17, 2026

   “Here, we carried out a controlled pilot-scale study of hot water systems and applied shotgun metagenomic sequencing to examine the effects of copper dose (0–2 mg/L), orthophosphate corrosion control agent, and water heater anode materials (aluminum vs magnesium vs powered anode) on the bulk water and biofilm microbiome composition. Metagenomic analysis revealed that, even though a copper dose of 1.2 mg/L was required to reduce Legionella and Mycobacterium numbers, lower doses (e.g., ≤0.6 mg/L) measurably impacted the broader microbial community, indicating that the OP strains colonizing these systems were highly copper tolerant. Orthophosphate addition reduced bioavailability of copper, both to OPs and to the broader microbiome. Functional gene analysis indicated that both membrane damage and interruption of nucleic acid replication are likely at play in copper inactivation mechanisms. This study identifies key factors (e.g., orthophosphate, copper resistance, and anode materials) that can confound the efficacy of copper for controlling OPs in hot water plumbing.”