The boroughs of Manhattan and Bronx , of an estimated population of 2,200,000 are dependent almost entirely upon the Croton River for their supply of water ; in fact , they have no other supply , except the comparatively small quantity ( 20,000,000 gallons per day ) from the Bronx and Byram Rivers , small as compared with 290,000,000 gallons , the present daily consumption of these two boroughs . The natural flow of Croton River in dry seasons was judged insufficient to supply the city as early as 1843 , now more than 60 years ago , so Croton Lake of a capac- ity of two billion gallons , was then created by building the old Croton Dam . Since then , from time to time , six other reservoirs , having an aggregate capacity of 40,000,000 , - 000 gallons , have been built on the principal tributaries of the river , above the lake , for the purpose of collecting water in wet seasons , to be discharged into the lake as re- quired for use . The city has no auxiliary supply , and no lakes or rivers that could be used as such in case of an emergency , hence an accident to a reservoir might result in so great a loss of water as to cause a water famine , truly styled one of the world's greatest disasters . The new Croton dam is located about thirty - seven miles from the Central Park reservoirs , it is on the Cro- ton River , about two and one - half miles below the old Croton dam . Its purpose is to enlarge Croton Lake , in- creasing its capacity from two to thirty - two billion gallons and its length from five and one - half to nineteen and three- quarter miles .