Reports of the results of water analysis are too often regarded as being of too technical a nature to be practically useful; whereas, on the contrary, such reports should at least indicate to the reader in what direction alterations, if necessary, in the present conditions of supply should proceed. With this object in view, I have endeavoured to include in the mom of the book the more recent conclusions which have been arrived at by workers in different branches of the subject, and have as far as possible refrained from details. Whilst it is necessary that the results of a chemical or bacterio logical analysis oi a sample of water should be intelligible to a non-professional reader, it need hardly be pointed out that it is impossible for any but those who have been trained in the methods of analysis to arrive at results which are worthy of confidence. This little book will have achieved an important result if it tends to make more generally known the fact how valueless — and, moreover, how dangerous — it is to rely upon so-called rough-and ready tests for forming an opinion upon the purity of a doubtful water.