7,077,700,000 — 7,716,500,000 = - 638,800,000 6,989,900,000 — ” = - 726,600,000 7,879,000,000 — ” = + 162,500,000 6,816,000,000 — ” = - 900,500,000 982,000,000 — ” = - 6,734,500,000 1,449,800,000 — ” = - 6,266,700,000 10,890,000,000 — ” = +3,173,500,000 7,373,100,000 — ” = - 343,400,000 4,032,900,000 — ” = - 3,683,600,000 5,178,500,000 — ” = - 2,538,000,000 4,343,100,000 — ” = - 3,373,400,000 5,126,300,000 — ” = - 2,590,200,000 --------------- --------------- -27,795,700,000 +3,336,000,000 + 3,336,000,000 --------------- -24,459,700,000 It is seen from this table that the total monthly deficiencies aggregate 27,795,700,000 gallons and that there are only two months in which the run-off exceeds the consumption, the surplus for those two months being only 3,336,000,000 gallons. The total deficiency for the year is therefore 24,459,700,000 gallons. Dividing the latter quantity by the average daily draft of 253,000,000 gallons, there will result a period of 97 days, or more than one quarter of a year, during which the minimum annual rainfall would fail to supply any water to the city at all. These results show that in case of a low rainfall year, like that of 1880, the precipitation upon the Croton watershed would supply sufficient water for the boroughs of Bronx and Manhattan at the present rate of consumption for three fourths of the year only. A distressingly serious water famine would result unless the year were begun by sufficient available storage in the reservoirs of the basin at least equal to 24,459,700,000 gallons. Should such a low rainfall year or one nearly approaching it be one of a two- or three-year low rainfall cycle, such a reserve storage would be impossible and the resulting conditions would be most serious for the city. If an average year, for which the total rainfall would be about 48 inches preceded such a year of low rainfall, the conditions would be less serious. The figures would stand as follows: Total run-off = 17,377,536 × 360.4 × 22.93 - 17,377,536 × 16.1 × 39.2 = 132,640,000,000 gallons. Total annual consumption = 92,345,000,000 ” --------------- Available for storage = 40,295,000,000 ” Deficiency = 24,459,700,000 ” --------------- Surplus = 15,835,300,000 ”