aqueduct of filter mains of single and double pipeage constructed at an initial plant cost of � 5 per linear yard by way of the Dargle, Rathdown, Glen of the Downs and Callowhill to the 26 acre reservoir at Stillorgan, a distance of 22 statute miles, and thence, through a system of relieving tanks, by a gradient of 250 feet to the city boundary at Eustace bridge, upper Leeson street, though from prolonged summer drouth and daily supply of 12 1/2 million gallons the water had fallen below the sill of the overflow weir for which reason the borough surveyor and waterworks engineer, Mr Spencer Harty, C. E., on the instructions of the waterworks committee had prohibited the use of municipal water for purposes other than those of consumption (envisaging the possibility of recourse being had to the impotable water of the Grand and Royal canals as in 1893)