More than 50 years after the Safe Drinking Water Act was passed to ensure that Americans’ water is free from harmful bacteria, lead and other dangerous substances, millions of people living in mobile home parks can’t always count on those protections.

A review by The Associated Press found that nearly 70 percent of mobile home parks running their own water systems violated safe drinking water rules in the past five years, a higher rate than utilities that supply water for cities and towns, according to Environmental Protection Agency data.

The problems may also be even bigger because the EPA database doesn’t monitor all parks.

Even where parks get water from an outside source — such as a city — the clean water coming in can become contaminated if it passes through problematic infrastructure before reaching residents’ taps. Because the EPA doesn’t generally require this water to be tested and regulated, the problems may go unseen, analysts say.

Utah is one of the few states to step in with their own rules, according to an AP survey of state policies.

“If you look back at the history of the Safe Drinking Water Act, like in the ’70s when they were starting, it was, ‘Well, as long as the source … is protected, then by the time it gets to the tap, it’ll be fine.’ And that’s just not how it works,” said Colt Smith of Utah’s Division of Drinking Water.

In one Colorado mobile home park, raw sewage backed up into a bathtub. In a Michigan park, the taps often ran dry and the water resembled tea; in Iowa, it looked like coffee — scaring residents off drinking it and ruining laundry they could hardly afford to replace. In California, boxes of bottled water crowd a family’s kitchen over fears of arsenic.

Almost 17 million people live in mobile homes.

The country has about 50,000 water utilities, most serving small towns and rural areas. Many struggle to find staff and funding, and they violate clean water rules more often than the handful of large utilities that serve cities.

The AP analysis found that more than half of the parks failed to perform a required test for at least one contaminant, or failed to properly report the results, in the past five years.