SHOULD first be stated that the views and opinions hereinafter outlined on this subject are not presented by the writer as being official lior as having already been adopted by the Department of Water Supply, Gas and Electricity as part of a definite program for the protection and maintenance of the water supply under war conditions. The problems involved in this matter for New York City are so vast in scope and of such varied nature that the Department has not even begun to formulate such a definite program, although certain steps for the protection of the system have already been taken, as hereinafter described. It need hardly be stated here that during time of war it is particularly important to maintain an adequate water supply to fight fires, as well as for domestic, industrial and sanitary needs. The general measures to be taken toward this end, as herein discussed, are those which would suggest themselves to every engineer engaged in the maintenance and operation of a water system, and are applicable to, and may be adopted by, cities other than New York City, although possibly on a smaller scale^ With the exception of large scale filtration works, there is included in the New York system every structure and facility existing anywhere for the collection, storage, transportation, treatment and distribution of water for the needs of domestic service and fire protection. Although the general features of this system are probably known to most engineers, it might be well, here, to present a brief description of its characteristics as a basis for a clearer understanding of the particular problems involved.