The water flowing sound in a household water heater typically stems from sediment accumulation, air pockets, or internal component vibrations. Sediment, often from hard water, settles at the tank's bottom, creating turbulence as heated water circulates. Air entering the tank through a faulty pressure relief valve or vent stack can also cause gurgling noises. Additionally, loose internal parts, such as the anode rod or dip tube, may vibrate against the tank walls during heating cycles.

Sediment buildup is the most common cause, as hard water minerals like calcium and magnesium react with heat, forming deposits. The U.S. Environmental Protection Agency (EPA) estimates that 85% of American households experience hard water, contributing to 95% of water heater noise complaints. A study by the American Water Works Association (AWWA) found that sediment layers exceeding 1 inch (2.5 cm) can reduce heating efficiency by 15% and amplify noise. The anode rod, which protects the tank from corrosion, may corrode over time, causing metallic vibrations. The AWWA reports that anode rods typically last 5–10 years, with premature failure linked to low water pH or electrical surges. A damaged dip tube, which directs cold water to the bottom of the tank, can disrupt flow, creating turbulence. Manufacturer data suggests dip tubes degrade after 5–10 years, often due to chemical corrosion or physical wear. Addressing these issues—flushing the tank, replacing the anode rod, or repairing the dip tube—can eliminate 80–90% of related noises, according to a 2021 Journal of Building Engineering study. Regular maintenance, such as annual flushing, is recommended to prevent recurrence.