Quick Answer:
If your hot water looks cloudy after refilling the tank, it’s commonly trapped air or disturbed sediment. First, run and observe taps, then follow the steps below to flush the tank and check clarity. In most cases a full flush clears the cloudiness; if it doesn’t, call a pro.
Why This Happens
When a heater is drained and refilled, air gets pushed into the plumbing and tiny bubbles make hot water look milky. Sediment or mineral scale on the bottom of the tank can also be stirred up and carried into the lines, showing as cloudy or gritty water. Occasionally the issue points to corrosion or dissolved metals, which is a different problem.
If you see surface residue or a slick after use, check information about Hot water leaves oily film. If the hot water has a metallic smell or taste, read about Hot water tastes like pennies.
Step-by-Step What to Do
Step 1 — Check which taps are affected
- Open a cold tap and a hot tap at the same fixture. If only the hot side is cloudy, the heater is the likely source.
- Note whether the water clears after a minute of running; air often clears quickly.
Step 2 — Prepare the heater for draining
- Turn off power: switch off the breaker for electric heaters. For gas units, set the control to “pilot” or “off” per the manufacturer’s label; if unsure, skip and call a pro.
- Turn off the cold-water supply to the heater.
- Open a hot-water tap to relieve pressure and allow air into the system during draining.
Step 3 — Drain and flush the tank
- Attach a hose to the heater drain valve and run it to a safe drain location that won’t be damaged by hot water.
- Open the drain valve and let the tank empty. Once empty, briefly open the cold-water supply to flush out sediment until the water runs clear at the drain.
- Repeat as needed. Flush heater fully and retest clarity.
Step 4 — Refill and retest
- Close the drain valve, remove the hose, and open the cold-water supply slowly so the tank refills without trapping air. Keep a hot tap open until water runs smoothly with no sputtering.
- Restore power or gas controls after the tank is full and you have no visible leaks.
- Run hot water at several fixtures to confirm clarity. If cloudiness persists, note color, smell, or particles before calling help.
What Not to Do
- Do not use cloudy hot water for cooking.
- Do not ignore metallic smells or brown/black water; those can indicate corrosion or contamination.
- Do not attempt complex gas valve adjustments or repairs if you are not trained; call a licensed technician.
- Do not pour drained hot water where it can scald people, pets, or damage surfaces.
When to Call a Professional
- Cloudiness won’t clear after flushing and running taps for several minutes.
- Water is discolored (brown, black) or has a metallic taste or smell.
- You find sediment, grit, or particles that persist despite flushing.
- The drain valve or other components leak, or you’re uncomfortable shutting off power or draining the tank.
Safety Notes
- Always turn off electrical power at the breaker for electric heaters before opening panels or valves.
- Be cautious with hot water to avoid scalding; allow the tank to cool if possible before draining large volumes.
- Wear gloves and eye protection when handling drain valves or working around hot pipes.
- If you smell gas or suspect a gas leak, evacuate and call your gas company or emergency services — do not operate switches or ignition sources.
Common Homeowner Questions
- Why did it clear after a minute at the tap? Small air bubbles often disperse quickly, which makes water look cloudy briefly.
- Is cloudy hot water harmful? If it’s just air, no; if it’s sediment, discoloration, or metallic taste, don’t drink it and get it checked.
- How often should I flush the tank? For households with hard water, once a year; otherwise every 1–3 years helps prevent sediment build-up.