The U.S. Military, at large, is responsible, not just one Branch. The water quality at almost ALL of our military installations has been suspect for decades. But I don't think it was intentional. The use of lead paint, lead window sills, asbestos floor/ceiling tiles, etc was common practice worldwide for decades. Most of the bases in this country were built with those items, then had to be decontaminated to allow go continued use today. It would stand to reason that those substances have leeched into the ground water supply thru improper disposal techniques, poor management, etc. Then tie in the fact that underground fuel tanks on our military bases that end up rotting and leeching fuel into the groundwater supply within 50 yrs of installation, and you have a recipe for disaster. Now add to that all of the people who have ever seen bed on these bases also disposing of hazardous chemicals in a bad manner, and you now see the issue.

Edit: a few cases I personally know of.

1. My time @ NATTC MILINGTON, TN to start with. My first barracks was condemned by NAVOSH, OSHA, AND EPA for toxic levels of lead paint, lead window sills, and asbestos ceiling/floor tiles. They had signs on the barracks walls. We were told not to sweep/mop the floors or move ceiling tiles, and not to open or touch the windows. The glass had lead, too. And I was hiis d in there for over a month before they finally moved us.
2. A NAVADMIN/MARADMIN came out around the '00-01 time frame (when I was stationed at MCAS BEAUFORT, S.C.) advising all Marines/Sailors housed at MCAS CHERRY POINT and MCB CAMP LEJEUNE re: groundwater contamination of lead, carcinogens from hazmat, and fuel. The Navy/Marin Corps had to pay for water bubblers for EVERY barracks room and military housing for cooking and drinking.
3. NAS Lemoore, CA had the same problem as Cherry Point. They now have bubblers and daily deliveries of 5Gal water jugs to each and every home on the base. Same with MCAS Miramar, CA, MCAS 29 Palms, CA.
4. Tinker AFB has the same issues. So do some Army bases, although I admit I can't remember which ones.
5. On of the reasons why Homestead AFB was clos d after Hurricane Andrew in '92 was because of contaminated ground water.

The problem is endemic among military bases, and not just U.S. bases. The British military, Indian military, and Canadian military have these problems, too.

The U.S. Military, at large, is responsible, not just one Branch. The water quality at almost ALL of our military installations has been suspect for decades. But I don't think it was intentional. The use of lead paint, lead window sills, asbestos floor/ceiling tiles, etc was common practice worldwide for decades. Most of the bases in this country were built with those items, then had to be decontaminated to allow go continued use today. It would stand to reason that those substances have leeched into the ground water supply thru improper disposal techniques, poor management, etc. Then tie in the fact that underground fuel tanks on our military bases that end up rotting and leeching fuel into the groundwater supply within 50 yrs of installation, and you have a recipe for disaster. Now add to that all of the people who have ever seen bed on these bases also disposing of hazardous chemicals in a bad manner, and you now see the issue.