Earlier this summer, after being closed for 40 years, the High Bridge, formerly an aqueduct, re-opened to public pedestrian traffic. Spanning the Harlem river at the northern edges of the Bronx and Manhattan, it was originally constructed in the mid-1800's to meet the growing demand for fresh water in response to the City's explosive industrial and residential growth at that time.
Construction of the High Bridge was completed in 1848, bringing fresh water from the Croton River, 40 miles away in Westchester county to an increasingly thirsty city.. Over 100 feet high and close to 2000 feet in width, it was considered to be a major engineering feat at the time, 
Yet, less than 20 years later, demand was already outpacing the capacity of the High Bridge's two original 3-foot pipes, and a 7.5-foot one was added. The aqueduct remained in service until the 1950s.
This pattern of escalating demand for water continues unabated even today. Two major projects-- the High Bridges of our time-- have been undertaken to meet this challenge. One is the Third Water Tunnel and the other is the Croton Water Filtration project.
In 1954 the City recognized and began planning for ways to improve the dependability of the City's water supply system. In 1970 construction finally began on the Third Water Tunnel. This project is not expected to be completed until 2020. Like the High Bridge, the source of the water flowing through it also originates in Westchester county. At a cost of 6 billion dollars and a length of 316,800 feet (or 60 miles) it will ultimately have the capacity to deliver 1.3 billion gallons of water daily to NYC residents. It is considered to be one of the "...largest and most complex public works projects ever attempted", not only in the city, but the country as well.
The Croton Water Filtration Plant, on the other hand, began construction seven years ago and was just completed and brought online this past May. It is located under a section of Van Cortlandt Park in the Bronx, "inside an excavated area big enough to hold Yankee Stadium". Again, like the High Bridge once did, it will bring water from the Croton watershed and is capable of treating as much as 290 million gallons of water a day, about one-third of the total daily citywide demand. Understandably it too has been cited as one of the largest construction projects in the City’s modern history.
However, will projects of even this colossal scale be enough to slake the City's thirst? If the past is any indication, maybe only for just a little while. According to the census, the City's population continues to grow, and faster than original estimates anticipated. At 8.5 million people, it has already surpassed projections for 2020!
At some point the City may just finally reach its limits-- either that of ingenuity or of nature.
