Southwest Water Co. said Monday that the California Public Utilities Commission approved an 11 percent rate hike, which should add $5.5 million to revenue.

The Los Angeles provider of water and wastewater services to cities, utility districts and private companies in eight states, said the increase would be retroactive to Jan. 1 and was due to changes in the utility’s cost structure.

The company late Friday said it would delay filing its annual report with the Securities and Exchange Commission because of errors that had been discovered related to the rate of depreciation of acquired assets, and revenue and costs associated with the installation of water and sewer taps.

The company’s shares closed down 30 cents or 6.7 percent to $4.20 on the Nasdaq.