Here is a number that stopped me cold when I first read it. Phoenix water contains arsenic at levels that are more than 1,026 times above the Environmental Working Group's health guideline. One thousand and twenty-six times. Let that sit for a second.
Now here is the part that matters: Phoenix water still meets the legal federal standard for arsenic. That is because the federal legal limit and the health-based guideline are two completely different numbers. The law allows arsenic levels that health scientists consider unsafe, because removing arsenic from a city water supply is expensive and difficult at scale.
That does not mean you have to drink it. A reverse osmosis system removes arsenic at your tap for pennies per gallon. But first you need to understand what you are dealing with.
What Arsenic Is
Arsenic is a naturally occurring element found in rock and soil. It is not something someone put in the water on purpose. It seeps into groundwater as water flows through arsenic-containing rock formations. Arizona has three natural geological sources of arsenic, which is one of the main reasons Arizona water supplies have higher arsenic levels than most other states.
Arsenic is tasteless and odorless. You cannot tell it is there. The only way to know your arsenic level is to test for it.
What Arsenic Does to the Body
Arsenic is a known human carcinogen. The EPA and the World Health Organization both classify it as a Group 1 carcinogen, which means there is clear evidence it causes cancer in humans. Long-term exposure to arsenic in drinking water is linked to:
- Bladder cancer (one of the strongest links)
- Lung cancer
- Skin cancer
- Kidney cancer
- Liver cancer
- Cardiovascular disease
- Diabetes
- Nerve damage
- Skin problems including dark spots and thickening
The risks are dose-dependent, meaning the more arsenic you are exposed to and the longer the exposure, the higher the risk. Children are more vulnerable than adults because they drink more water per pound of body weight and their developing systems are more sensitive.
Why the Legal Limit Is Not the Same as a Safe Limit
The EPA's legal limit for arsenic is 10 parts per billion. The EWG's health guideline, based on cancer risk calculations, is 0.004 parts per billion. That is a gap of 2,500 times between what the law allows and what scientists believe is safe.
The EPA acknowledges this. They set the legal limit at 10 ppb because that is the lowest level they can realistically require water utilities to achieve given the cost and technology constraints of treating city water at scale. In their own words, they had to balance "the current understanding of arsenic's possible health effects against the costs of removing arsenic from drinking water."
Phoenix water has been measured at around 4 to 7 parts per billion. That is within the legal limit. It is still thousands of times above what health researchers consider a no-risk level.
Arsenic and Well Water in the Phoenix Area
If your Phoenix area home uses a private well in places like Apache Junction, Queen Creek, New River, Cave Creek, or Wittmann, your arsenic exposure risk is higher. Private wells are not regulated by the EPA's drinking water standards. They are also more likely to draw from groundwater that has traveled through arsenic-rich rock formations.
If you are on well water, testing for arsenic is not optional. It is something you should do every year. Many Phoenix area well owners have never tested and have no idea what their arsenic levels are.
How to Remove Arsenic From Your Drinking Water
A certified reverse osmosis system removes arsenic very effectively. Most quality RO systems reduce arsenic by 90 to 99 percent. The membrane blocks arsenic molecules the same way it blocks PFAS, lead, nitrates, and other dissolved contaminants.
Standard carbon filters do not remove arsenic. Pitcher filters do not remove arsenic. A Brita filter does not remove arsenic. You need a reverse osmosis system certified to NSF/ANSI Standard 58 for arsenic removal.
This is exactly why our Complete Home Water package includes a free AlkaPro 800 tankless reverse osmosis system with every whole-home softener. The RO system sits under your kitchen sink and filters the water you drink and cook with down to near-zero arsenic levels.
A Quick Note on Arsenic and the EWG Tool
The Environmental Working Group has a free tool at ewg.org/tapwater where you can look up your specific water utility and see exactly what has been detected in your water and at what levels. It is worth five minutes of your time to see what is actually in your water.
Worried about arsenic in your Phoenix drinking water? Call us or fill out the form. Our free on-site water test on install day tells you exactly what is in your water. We serve Gilbert, Mesa, Chandler, Tempe, Scottsdale, Phoenix, and the entire East and West Valley.