In this new edition of a well known laboratory guide, there has been little change in the chemical analyses described; but the tests for "relative stability," free chlorin, and lime and soda values have been added. The bacteriologic methods have been rewritten to conform to the latest edition of "Standard Methods." Unfortunately the normal chlorin maps referred to in the text have been omitted. The illustrations have been materially improved over those in former editions. Amplification of Appendix A, discussing the interpretation of a water examination, would greatly increase the usefulness of the book for elementary students.