The tower was built in the Baroque style in 1658 on what remained of the original Renaissance tower, destroyed by a flood in 1655. It supplied water to the lower New Town of Prague and served its original purpose until 1877. The Tower has undergone a complete renovation, and now houses an exhibition about Prague’s fires in the past and a history of Prague’s fire-fighters.
Source: https://www.prague.eu/en/object/places/2858/the-city-of-prague-museum-the-new-mill-water-tower