This paper discusses a few of the many serious and complex water quality problems confronting water users in California. For ease of presentation and discussion, these water quality problems are broadly grouped under conditions of pollution caused by sewage and industrial waste disposal, and degradation caused by man's development and use of the water itself. Minor quality of water problems resulting from natural causes are also recognized and discussed.

As the authors point out, the major unsolved problem in California is: How can the perpetual usability of ground‐water basins as reservoirs for fresh water storage be assured? This implies that the ground‐water basins, when used for storage of surplus surface waters, must be alternately emptied and filled, and that an economical method to accomplish this must be devised. If these requirements cannot be met, the fundamental conclusion, “… that the State's water resources … may be adequately regulated … to meet its probable water requirements without importation of water from a source outside the State of California …” may be seriously in error.