Rusty, cloudy, or blue-green hot water
How to tell tank rust from a disturbed water main, aerated water, copper corrosion, and slime in an aerator.
Color in the water is a location problem. Rust only in the hot tap points at the heater or the steel nipples on it. Rust in both hot and cold points at the supply, the well, or galvanized piping in the house.
A milky glass that clears from the bottom up is usually air. Blue-green stains are usually copper corrosion downstream of the heater. Pink slime on an aerator is usually a surface bacteria that never saw the tank.
Treating all of these as “the water heater is dying” sells heaters. Missing the one pattern that really is a dying heater floods a closet six months later. Smell is a separate page, rotten eggs, unless the color and the smell arrived together, in which case read both.
Rust only when the tap is hot
Run cold water into a white cup for a minute. Run hot into another. If the cold is clear and the hot is brown, yellow, or full of grit, the steel involved is on the hot side.
The sacrificial anode is supposed to corrode instead of the tank. When the rod is gone, the glass lining’s pinholes become rust.
You may still have a dry floor. Color is an early announcement, not proof that the shell has already perforated. Inspect or replace the anode now, using the anode guide.
If the rod comes out as a thin wire, it was overdue. If the port threads are already wrecked, the tank is further along than a new rod can save.
Steel nipples and dip tubes also make rust-colored water while the shell is intact. A plumber who pulls the inlet and finds a disintegrated nipple can sometimes replace fittings and the anode and give the tank more years.
If the outlet fitting’s threads in the tank are corroded, the honest call is replacement. Do not keep drawing brown water because the floor is dry. Rust in the stream means steel is leaving, and the repair or replace question should be priced while you still have a choice of dates.
A flush can release a slug of brown water that clears. That is sediment, not a new hole. Warn the household, flush until clear, and do not wash white clothes that afternoon.
The procedure is the flush. If the water stays brown for days after a careful flush, you are back to the anode and the shell.
Rust in both taps
If cold is also brown, the heater is not the source, even if the hot looks worse because heat changes how the particles behave. Municipal work on the main, a hydrant flushing program, or a well that just pumped sand will color every tap.
Let the cold run at a tub, not through a filter cartridge you care about, until it clears.
If it does not clear, call the water supplier or the well contractor. A new heater installed into a rusty supply will be rusty immediately and the anode will be blamed for someone else’s main.
Galvanized steel house piping rusts from the inside and sheds into both temperatures, often worse when a faucet that is rarely used is opened. The pattern is a particular bathroom, or the whole house, including cold. Replacing the heater does not replace the pipes.
If only the pipes near the heater are galvanized and the rest of the house is copper, the short galvanized nipples can still be the entire problem. Look at what the pipes are made of before you buy a tank.
Cloudy water that clears
Fill a glass and watch it. If the milkiness starts at the bottom and clears upward over a minute or two, the cloud is fine bubbles of air coming out of solution.
It is common after plumbing work, after a flush, or when a new aerator is swallowing air. It is harmless. If the cloud does not clear, or it settles as white grit, you are looking at minerals or at a failing dip tube’s plastic crumbs.
White grit that looks like sand is often calcium from hard water, or a water-softener problem sending resin beads down the line. Resin beads are small amber spheres, not rust. A softener that has dumped resin needs service. The heater did not invent the beads.
Blue-green stains and pink slime
Blue or green staining at a fixture, sometimes with a metallic taste, is copper corrosion. Low pH water, high velocity, and electrical grounding issues on the plumbing can all eat copper pipe and valves. The water heater’s glass-lined tank is not a copper part, so a new tank will not stop a low-pH well from staining the tub.
Get the water tested and ask a plumber about dielectric protection and whether the water needs treatment. This site does not prescribe a chemical treatment program from a stain color. A certified lab number beats a guess.
Pink or orange slime on an aerator, a showerhead, or a toilet reservoir is commonly an airborne bacteria that colonizes wet surfaces, often called pink mold in hardware-store language and often not mold. Clean the aerator in a vinegar soak, flush the screen, and dry the fixture.
If it returns only at one sink, the tank is innocent. If the slime is throughout a little-used bathroom, use the fixtures more often so water does not sit, and clean. Persistent slime plus a sulfur smell belongs on the smell page as well, because a fixture can host both problems.
| What you see | Where | Likely source | Useful next step |
|---|---|---|---|
| Brown or yellow | Hot only | Anode gone, tank or nipples | Inspect the anode. Plan on replacement if threads are bad. |
| Brown | Hot and cold | Main, well, or galvanized pipe | Run cold. Call the supplier if it persists. |
| Brown slug, then clear | Hot, after a flush | Disturbed sediment | Finish the flush. Do not do laundry yet. |
| Milky, clears from the bottom | Either | Dissolved air | Wait. No parts. |
| White grit or beads | Either | Scale or softener resin | Hard-water page, or softener service |
| Blue-green stains | Fixtures | Copper corrosion | Water test. Not a new tank by itself. |
| Pink slime | Aerator | Surface bacteria | Clean the aerator. |
What not to pour into the tank
Do not dose the heater with acid to “dissolve the rust.”
You will attack the lining and the anode and you may push a plug into a fixture. Do not install a cartridge filter on the hot outlet and consider the problem solved if the anode is gone. The filter will clog, and the tank will continue to perforate.
A filter is reasonable as a short bridge while you schedule the repair, if you change it before it bursts. Do not ignore rust because a water test from five years ago was fine. Anodes are consumables. The interval is in the anode guide, shorter on softened water.
If a brand-new heater is producing rust in the first week, call the installer. A new tank can shed a little manufacturing residue on the first heat, and it should clear.
A new tank that runs rusty because the old galvanized nipples were reused is an installation defect. Photograph the piping. The labor warranty is the path, and it is often short. The lifespan page explains how those warranties are structured so you ask while the coverage exists.
Sources
Manufacturer guidance on anode rods and discolored water (A. O. Smith, hotwater.com; Bradford White, bradfordwhite.com; Rheem, rheem.com). U.S. Department of Energy, Energy Saver, storage-tank service life, as context for why a rusty hot side on an older tank is a replacement conversation. Local water suppliers publish notices when hydrant flushing or main work will discolor tap water; those notices are the first check when both hot and cold run brown on the same morning.