Purification of Water Supplies

Abstract

The water supplies west of the Cascades are principally soft, low in alkalinity and with a pH ranging from slightly acid at high river stages, to slightly alkaline at low stages. The color of these waters varies with the rainfall and the amount of tributary swampy area. The turbidities are not high, as a rule, and are usually coarse except where glacial flour is present. After heavy rainfall particularly, turbidities may be present in objectionable amounts. East of the Cascades the waters the waters of the Pacific Northwest are much more alkaline, except those coming from the mountains themselves. They have a greater range of turbidities, and carry considerably more mineral matter. Though the purification of these waters is more necessary, the problem is a simpler one, since the water is more easily coagulated. This paper, therefore, will be limited to a discussion of the problems involved in the purification of the softer waters of the western slope. These are more like the waters of New England than of any other section of the United States, but are less colored and have higher alkalinities. The average water characteristics for a number of streams in Washington, with one analysis from Oregon, are shown in table 1. From this table the general character of the water on both sides of the Cascades can be seen.