Why was frontinus so proud of the roman water system?

Frontinus was appointed commissioner of the aqueducts. He had plenty of reasons to be proud of the aqueducts. They were a major engineering achievement. The Romans took the construction of these structures to a much higher level than previous or contemporary civilisations through their vast improvements in bridge-building technology. This allowed them to pace the water conduits on bridgeworks when they needed to cross a valley or, in flat areas, when they needed to keep a gradient to keep the water flowing. It enabled the Romans to build hundreds of aqueducts around their empire, a feat which had been previously impossible.

In addition to the above, aqueducts were essential to supply towns with fresh water from the sources on the mountains. The Romans built many aqueduct to supply a growing demand for water caused by Rome's expanding population.