A leaking water inlet valve in a toilet tank typically results from mineral buildup, mechanical wear, or misalignment, causing continuous water flow into the tank and potential overflow. Common causes include clogged or damaged valve components, worn-out O-rings, or incorrect installation. Addressing the issue involves replacing the valve, cleaning internal components, or adjusting its alignment to restore proper operation.

The primary reason for a leaking inlet valve is mineral deposits from hard water, which accumulate on internal components like the float mechanism or seat. According to the Environmental Protection Agency (EPA), hard water contributes to 30% of household appliance and plumbing failures, including toilet valve leaks. Over time, repeated water flow exacerbates wear on rubber seals and springs, leading to cracks or tears. Industry data from the American Water Works Association (AWWA) indicates that 25% of toilet leaks stem from faulty inlet valves, often due to neglected maintenance. Incorrect installation is another frequent cause, where improper seating or misalignment prevents the valve from sealing properly. For example, a 2021 study by the National Sanitation Foundation (NSF) found that 40% of toilet valve leaks in older homes (pre-2000) were linked to outdated valve designs or poor installation practices. Age-related degradation also plays a role, as valves typically last 5–10 years before requiring replacement. Proactive maintenance, such as annual descaling with vinegar or replacing worn parts, can mitigate these issues. In summary, addressing inlet valve leaks requires identifying the root cause—whether mineral buildup, mechanical failure, or installation errors—and taking corrective actions to prevent water waste and system damage.