What Causes Discolored Tap Water? Brown, Yellow, and Green Water Explained

Turning on the faucet to find brown, yellow, or greenish water is alarming. Most of the time it's not a health emergency — but it does require attention. Here's what each color means, what's causing it, and what to do next.

Brown or Rust-Colored Water

Brown water is the most common discoloration complaint and typically indicates one of three things:

1. Rust from Aging Pipes

Most likely cause in older homes. Galvanized steel pipes (common before 1960) corrode from the inside out. As the zinc coating wears away, iron oxide (rust) flakes into the water. Iron pipes in older municipal distribution systems do the same.

Signs it's pipe rust:

• Brown color only from hot water? → Water heater is likely the source (rusting tank)
• Brown from all faucets, hot and cold? → Could be main supply pipe or galvanized supply lines
• Happens only after water hasn't been used for hours → Rust that settled in pipes when water was still

What to do: Run cold water for 2–3 minutes. If it clears, it's stagnant rust from sitting pipes — not harmful but a sign of aging infrastructure. If it doesn't clear after 5 minutes of running, call a plumber.

2. Utility Main Work or Disturbance

Fire hydrant flushing, water main breaks, or pressure surges from utility work stir up sediment in municipal distribution pipes. This is very common and completely harmless — the utility should notify customers before flushing, but not always.

Signs it's a utility issue:

• Brown water from all faucets simultaneously
• It started suddenly after a quiet period
• Neighbors have the same issue

What to do: Check your utility's website or social media, or call their customer service line. Run cold water until it clears. Don't run the hot water heater — stirring sediment into the tank is a nuisance.

3. Water Heater Sediment

If brown water comes exclusively from the hot water tap, the water heater is almost certainly the source. Sediment (calcium, magnesium, and iron minerals) settles at the bottom of the tank and gets stirred up, especially as the anode rod deteriorates.

What to do: Flush the water heater — attach a garden hose to the drain valve, open it, and let water run until it's clear. If the problem persists or the anode rod is spent, call a plumber to service or replace the heater.

Yellow Water

Yellow water is usually a milder version of brown water — lower rust or mineral content, or:

Iron or Manganese in Well Water

Private well owners commonly see yellow or yellow-brown water, especially after heavy rain that disturbs aquifer sediment. Manganese specifically produces a yellow-brown color and is a regulated contaminant above 0.05 mg/L.

What to do: Test the well water for iron, manganese, and total dissolved solids. Iron filters or oxidizing filters (like a whole-house iron filter) resolve most well water discoloration.

Chlorine Interaction

Municipalities use chlorine and chloramines to disinfect water. In areas with higher iron content in the distribution system, chlorine can oxidize dissolved iron, causing yellow color.

What to do: A whole-house filter with activated carbon addresses this. Run water until clear and let your utility know.

Green or Blue-Green Water

Green or blue-green water almost always indicates copper corrosion.

Copper Pipe Corrosion

As copper pipes corrode, they leach copper ions into the water. At low levels, this produces a slightly blue or green tint. At higher levels, it's a health concern — the EPA action level for copper is 1.3 mg/L.

Signs of copper corrosion:

• Blue-green stains around sink and tub drains
• Green tint most noticeable when filling a white tub
• Happens in newer homes with copper plumbing

Causes of copper corrosion: Low pH (acidic) water, high dissolved oxygen, certain disinfectants, water velocity, or galvanic action between dissimilar metals.

What to do:

• Test water pH — if below 6.5, the water is too acidic and attacking your copper pipes
• Call your utility if on city water; they're responsible for maintaining proper pH
• For well water, a neutralizing filter (calcite filter) raises pH and stops corrosion
• Run water for 30 seconds before use if the home has sat empty

Algae (in Storage Tanks or Old Plumbing)

Rare, but green water from algae growth is possible in homes with old underground cisterns or storage tanks. This is a serious issue — call a plumber or water treatment specialist.

White or Cloudy Water

White or milky water isn't discolored in the rust/mineral sense — it's almost always dissolved air bubbles.

Cause: Air entrapped in pressurized water supply (common after utility maintenance or pressure changes). The water looks white coming out but clears within 1–2 minutes as bubbles rise.

What to do: Fill a glass, wait 60 seconds. If the cloudiness clears from the bottom up, it's air — completely harmless. If it stays cloudy, it may be sediment or particulate — filter and test.

When Is Discolored Water Unsafe?

Probably fine (though unpleasant):

• Brown/rust that clears after running for a few minutes
• Cloudiness that disappears within 60 seconds
• Isolated episode after utility work

Requires testing/action:

• Discoloration that persists after running water for 5+ minutes
• Yellow-brown well water (manganese can cause neurological issues at high levels)
• Blue-green water from copper (potential health concern above EPA action levels)
• Any unusual color following flooding or natural disasters (contamination risk)
• Any color change accompanied by unusual smell or taste

Testing Your Water

If discoloration persists or you're on a well, test the water:

• Basic at-home kit: $10–$30, tests pH, hardness, iron, and basic metals
• Mail-in lab test: $30–$100, provides comprehensive results including bacteria, nitrates, heavy metals
• Certified lab test: Recommended for wells — contact your state health department for a certified lab list

The EPA recommends private well testing annually for bacteria and nitrates, and every 3 years for a comprehensive panel.

Long-Term Fixes for Recurring Discoloration

Problem	Solution	Cost
Galvanized pipe corrosion	Repipe with PEX or copper	$2,000–$15,000
Water heater sediment	Annual flush + anode rod replacement	$0–$250
Iron in well water	Iron filter / oxidizing filter	$500–$2,000
Copper corrosion (low pH)	Neutralizing filter	$500–$1,500
High manganese	Oxidizing filter + softener	$800–$3,000
Utility main issues	Report to utility; not your problem to fix	$0

Discolored water is worth investigating promptly — especially in older homes with original supply pipes. A licensed plumber can diagnose whether the issue is in your system or the utility's, and recommend the appropriate fix.