Healthy living conditions require pure and adequate supplies of air and water, the satisfactory and hygienic disposal of solid liquid and gaseous wastes, and the control of all forms of pollution. Public Health Engineering, or Environmental Health Engineering as it is sometimes called, comprises the construction and operation of the works needed to maintain such conditions. Whether we be dealing with the supply of water, the disposal of garbage, or the suppression of noise or smoke, a combination of internal and external works is almost invariably needed to obtain the required results, and I think this paper will be found to be very largely complementary to the other papers heard today. The principal public health engineering services inside buildings include water storage and distribution systems, sanitary installations, space-heating systems, air-conditioning installations, and refuse-collection systems. The major external works include schemes for the abstraction, treatment and distribution of water, for foul and storm drainage, for the disposal of sewage and trade effluents, and for the conveyance and disposal of refuse.