One factor affecting the quality of water for the 4 million water users in the Santa Ana River Watershed is the adverse salt balance that exists in the basin. An adverse salt balance, or high total dissolved solids (TDS), is the result of more minerals or salts entering a watershed than going out. Salt is added to the Santa Ana River watershed by fertilizers and chemicals, and by the import of water with higher levels of salt.
In addition, municipal, industrial and agricultural wastes increase the salt imbalance as does water reuse. Within the Santa Ana River Watershed, water is used at least twice before ultimate disposal to the ocean. These water uses concentrate the salts with each use. Typically, each use adds 200-300 mg/L TDS. TDS begin to interfere with the use of water somewhere between 500 and 1,000 mg/L. At 1,000 mg/L, water is brackish and unusable.