THE Census of Municipal Water Softening Plants in the United States (Journal A. W. W. A., 29: 1682 (1937)) and subsequent revised censuses mimeographed for private distribution by the author, only the name of the community having the installation was given together with the type of treatment zeolite or chemical precipitation. To provide more detailed data, then, a questionnaire covering important information on the various phases of treatment, loads, etc., was sent to all communities known to have water softening equipment. Information was received direct from water department officials, state departments of health, consulting engineers, manufacturers' representatives and private sources. It is printed as received and according to the author's interpretation in each case. In some cases it may be noted, by comparison with previous censuses, that names of communities previously shown to have water softening have been omitted from the accompanying tabulation. This is due to several factors wrong information, change in treatment, and abandonment of softening (in a very few cases, principally due to cost.) Figure 1 shows the growth of municipal softening in the United States from 1905 to the present. In the accompanying tabulation, the following states are not shown, no municipal softening plants in these states having been recorded : Connecticut, Idaho, Maine, New Hampshire, Oregon, Rhode Island, Tennessee, Utah, Vermont and Wyoming. The division of softening plants by areas is as follows: