The two sources definitely decided on in July, 1907, were those from Estanzuela and San Geronimo. The works were designed to supply 40,000,000 liters daily, which it was assumed would be sufficient for all future developments for a population of 200,000 at a per capita consumption of 200 liters per day. The present requirements of the city's population, assuming that all the water was supplied by the Company, would be, at that rate, which is a very liberal one, only 18,000,000 liters daily. This, it was thought, would be easily met by the San Geronimo source alone, as it was estimated that it would provide not less than 20,000,000 liters, if the infiltration gallery was driven far enough into the water-bearing gravels.
The question of a high-pressure water supply for domestic use in a city like Monterrey is not a serious one, as practically nine-tenths of the houses are of one story. The increase in the number of large commercial buildings, however, will make the demand greater in the future, and this point has been kept in mind in arranging the division of the distribution systems.
_Cement._--In the early stages of construction the cement for the work was obtained from the Associated Portland Cement Manufacturers, Limited, of London, which supplied the "Pyramid" brand, from the Knight, Bevan, and Sturges Works, but later the supply was obtained from a new factory at Hidalgo, near Monterrey. The total quantity of Portland cement used was 42,500 bbl. of "Pyramid" and 32,500 bbl. of "Hidalgo." The English cement was tested for the Water-Works Company in London before shipment and again at Monterrey, to conform to the British Standard Specifications; the "Hidalgo" cement was required to pass the Standard Specifications advocated by the Special Committee of the American Society of Civil Engineers. The quality in each case was of the very highest, no difficulties being experienced at any time.
_Sand and Rock._--One of the chief difficulties in connection with the construction work in its initial stages was in procuring satisfactory sand for the concrete. An investigation of the quality of all the available sands in the neighborhood of Monterrey resulted in the decision to use a manufactured sand obtained from the calcareous shales in the foot-hills opposite the city, on the south side, and near the site of one of the proposed reservoirs. A quarry was opened, and the raw material was delivered by a gravity plane to a crushing plant, 230 m. from the quarry and at a level about 50 m. lower.