This October marks 20 years since San Diego cut a famous deal that protected it from drought but paved the way for putting a high price on otherwise free water from the Colorado River.

The hard-fought deal – called the Quantification Settlement Agreement, or QSA – dramatically lowered how much water California takes each year from this river that makes life possible in seven western U.S. states and northern Mexico. It ensured, for the first time, that California wouldn’t use any more than its share. And it achieved that by putting a cap, for the first time, on how much water the farmers in Imperial Valley could take. Water officials would now meticulously count every gallon that once haphazardly emptied from farm fields into the Salton Sea. Today, that massive lake is in danger of becoming a massive public health and ecological disaster.