The Rainbow Municipal Water District serves a relatively rural group of customers.   However there are some areas of the District that are served by a public sewer system.

In the areas served by public sewer, the District is responsible for the facilities necessary to collect and transmit sewage from the District to a treatment plant located in Oceanside.  This is accomplished by a gravity flow system of collection pipes, six pumping stations, and a large transmission main to the San Luis Rey Wastewater Treatment Plant, located in Oceanside.

The District owns, through contract, capacity to treat one million gallons of sewage per day at the Oceanside plant.  Currently the plant is being rehabilitated and expanded and the District is participating in its contracted obligation to fund a proportionate share of the rehabilitation costs.  A contract has also been made to secure an additional 500,000 gallons per day of treatment capacity in the expansion portion of the project.

The District maintains the pipelines and pumping equipment from the District to the Oceanside plant.