She grew up in mountain mobile home parks. Now she’s running a bill to fix their foul water.

EDWARDS — When Elizabeth Velasco first moved to Colorado from San Francisco del Rincón, Mexico, she was a teenager living in a series of aging mobile home parks in Eagle County — very near the tony ski resorts of Vail and Beaver Creek, but also very far removed. As a 15-year-old, Velasco says she was definitely aware of water-quality issues that have plagued mobile home parks in the mountains for decades. But as a 34-year-old political newcomer working to unseat an incumbent Republican last year, Velasco became acutely focused on...