The Casitas Municipal Water District supplies water to 60-70,000 people in Western Ventura County and to hundreds of farms. The District boundaries encompass the city of Ojai, Upper Ojai, the Ventura River Valley area, the city of Ventura to Mills Road, and the Rincon and beach area to the ocean and Santa Barbara County line.

The District's current annual water deliveries can vary considerably from year to year. This is because the District has a large number of agricultural customers whose water needs can change significantly due to variations in weather and rainfall. Water deliveries can be lower than 15,000 acre-feet per year to higher than 23,000 acre-feet in a given year.

The District was formed in October of 1952. On March 1, 1956, the Ventura River project was authorized by Congress, which included the Robles Diversion facility on the Ventura River, the Robles Canal, and the Casitas Dam. The Casitas Dam was completed in November 1958. Lake Casitas then began to fill up and would not spill until 1978. Lake Casitas holds 254,000 acre-feet of water when full.