Last updated: July 2026 · Reviewed against A.O. Smith and Rheem service documentation
A leaking water heater drain valve is the most common repairable source of a bottom leak — and usually the cheapest to fix. The valve is the spigot at the base of the tank used to flush sediment. Most are plastic and turn brittle after 8–10 years, so the washer or threads give out and it drips. Here is how to confirm it and fix it, from a $3 temporary cap to a proper brass replacement.
Confirm It Is the Drain Valve
Water pools at the base from several possible sources, so confirm before you fix. Dry the valve completely, wrap a paper towel around it, and wait 30 minutes. A damp towel means the drain valve is your leak. If the towel stays dry but water still appears, the source is elsewhere — check our guide to a water heater leaking from the bottom for the other four causes.
Fix 1: Tighten or Cap It (Temporary)
First, try snugging the valve a quarter turn clockwise — gently. Do not force a plastic valve; overtightening cracks it and turns a drip into a flood. If it still weeps and you cannot replace it right away, screw a brass garden-hose cap ($3 at any hardware store) onto the valve outlet. This stops the drip at the opening as a stopgap until you do the real fix.
Fix 2: Replace the Valve (Permanent)
The proper fix is swapping the old plastic valve for a brass one ($10–$15). Steps:
- Turn off power/gas and the cold-water supply — see how to turn off your water heater.
- Attach a hose to the valve and drain the tank below the valve level (a few gallons).
- Unscrew the old valve counterclockwise.
- Wrap the new brass valve’s threads with PTFE (plumber’s) tape.
- Screw it in hand-tight plus a wrench turn, refill, and check for leaks.
If you are not comfortable draining the tank, a plumber will do this for $100–$200. Always choose brass over plastic for the replacement — it is the reason the original failed.
When to Just Replace the Heater
A drain valve leak on its own does not mean a new heater — it is a cheap part. But if the tank is over 10 years old and you are also seeing rust or leaks elsewhere, weigh the repair against replacement. A drain valve fix on an 11-year-old tank with other issues is buying months, not years.
FAQ
Can I use a water heater with a leaking drain valve?
Short-term, a slow drip from the drain valve is not an emergency, but cap or fix it promptly — the plastic can fail further and turn a drip into a significant leak. It will not damage the heater itself.
Why is my drain valve leaking after flushing the tank?
Very common: sediment gets caught under the seat when you close it, or the brittle plastic does not reseal. Try opening and closing it once to flush the debris. If it still drips, the valve needs replacing with a brass one.
What size is a water heater drain valve?
Most residential drain valves use a standard 3/4-inch garden-hose thread. Replacement brass valves at any hardware store fit the vast majority of tanks, but check your model if unsure.
Sources: U.S. Department of Energy — Water Heating · manufacturer service documentation (A.O. Smith, Rheem, Bradford White).