Salts in water can be measured by relatively simple methods.
One is by Electrical Conductivity (the reciprocal of electrical resistance) using an appropriate conductivity meter for the measurement. instruments are used by farmers and can be purchased relatively cheaply compared to most scientific instruments. For a historic background on this method there is a century-old paper by Whitney and Means, 1897 (USDA, Div. of Soils Bul. 7, 15 pp.) and our own USDA Handbook 60, 1954.
Another method involves weighing water in a weighing container, and evaporating the water, then re-weighing and determining weight/volume (by difference). This is a little tricky because a sensitive balance must be used, and high temperatures my volatilize some salts.
How do I find out about the importance of water in California?
In California, there are many publications and countless newspaper articles regarding water needs associated problems. A good summary is a special issue of "California Agriculture", 1984, Vol 38 (10). For current problems and concerns, another resource is a periodical magazine published by the Water Education Foundation, called "Western Water". Your local library can help you obtain copies of all mentioned references.