If your Phoenix tap water suddenly tastes like dirt or smells musty, usually starting in late summer and peaking in the fall, the cause is algae in the canals that carry water to the city's treatment plants. It's harmless, it's seasonal, and it's a known issue: the City of Phoenix describes it in its own water quality materials. The taste fades as temperatures cool, and an activated carbon or reverse osmosis filter removes it in the meantime.
Here's what's going on, why it happens every year, and what actually works.
Where the Musty Taste Comes From
About 97 to 99 percent of Phoenix's drinking water is surface water from the Salt, Verde, and Colorado rivers, according to the City of Phoenix's 2025 Water Quality Report. That water reaches the city's five treatment plants through open canals: the Salt River Project (SRP) canal network and the Central Arizona Project (CAP) aqueduct.
Open canals in the desert sun grow algae. The city's report says algae in the canals during late summer and fall are "a major source" of the musty odor and taste some customers notice. Algae and related organisms produce compounds such as geosmin and MIB, which people can detect at extremely low concentrations. That's why a small amount can change how a whole glass tastes.
The treatment plants remove the algae. The scent is harder. Phoenix compares it to taking a bouquet of flowers out of a room: the flowers are gone, but the smell lingers.
Is It Safe to Drink?
Yes. The City of Phoenix describes taste, odor, and hardness as harmless, aesthetic aspects of the water, and none of them are regulated as health standards. The city's 2025 report says Phoenix tap water met or surpassed all federal and state drinking water standards.
A musty taste is a quality-of-life problem, not a safety one. If your water tastes earthy and also looks discolored or cloudy, that's a different issue, and it's worth calling the city's water quality line at 602-262-6251.
For the full picture of what's in Phoenix tap water, read Is Phoenix Tap Water Safe to Drink?
Why It Happens in Late Summer and Fall
Algae need warm water and sunlight, and Phoenix canals get plenty of both through the summer. Growth builds over the hottest months, which is why the city says taste and odor variations are typically strongest near the fall. As temperatures drop, growth slows and the taste fades.
The city works on it at the source: SRP brushes its canals to reduce the algae, and Phoenix uses carbon at its treatment plants (much like a refrigerator filter) and blends CAP and SRP water to improve taste. It reduces the problem, but in a heavy algae season some of the taste can still reach your tap.
Is It My Pipes or the City's Water?
A quick way to tell:
- Musty or earthy in every faucet, mostly in late summer and fall: almost certainly the seasonal canal algae.
- Only in hot water: often your water heater. Flushing the tank can help.
- Only at one faucet: the drain or the faucet aerator may be the source. Smell the water in a glass away from the sink.
- Pool-like smell year-round: that's chlorine, the disinfectant Phoenix uses to keep water safe through the distribution system. It's a different taste from the earthy one.
How to Get Rid of the Musty Taste
Free fixes
The City of Phoenix's own suggestion: let water sit for a few minutes, or add a slice of lemon or lime. Chilling water in a covered pitcher in the fridge also makes the taste much less noticeable.
Activated carbon filters
Pitcher, faucet-mount, and refrigerator filters use activated carbon, the same material the city uses at its plants. Look for certification to NSF/ANSI 42, the standard for taste and odor reduction, and change the cartridge on schedule. An exhausted filter stops working.
Under-sink reverse osmosis
An under-sink RO system pairs carbon stages with an RO membrane. The carbon handles the earthy taste and the chlorine; the membrane removes the dissolved minerals. The City of Phoenix's 2025 report lists total dissolved solids of 464 to 716 mg/L, and that mineral load gives Phoenix water its heavy taste year-round. If the musty season is what finally sends you looking for a filter, RO solves all three tastes at once. Learn more in Reverse Osmosis Systems Explained.
What won't help
A water softener. Softeners remove calcium and magnesium (hardness); they aren't built to remove taste and odor compounds. Boiling won't reliably help either, and it can concentrate the minerals.
The Bottom Line
That earthy, musty taste in Phoenix tap water every fall comes from algae in the canals that feed the city's treatment plants. It's safe, it's seasonal, and it fades as the weather cools. If you'd rather not taste it at all, an NSF-certified carbon filter handles it, and an under-sink RO system handles it plus the chlorine and mineral taste that are there year-round.
Whale Spout Water installs 5-stage under-sink RO systems with alkaline remineralization for $899 fully installed. If you want to talk through whether you need one, book a free 15-minute consult.