Centennial Park Reservoir No.1 was the largest covered storage reservoir constructed in Australia at the time it was built and it remains very large by present-day standards. It is associated with the early development of the Upper Nepean Water Supply Scheme and the subsequent expansion of water reticulation throughout the suburban areas of Sydney. It is also associated with the rapid urban expansion of the eastern suburbs of Sydney in the late 19th century. The reservoir demonstrates exemplary engineering practices at the turn of the century in relation to design, construction methods and manual skills, particularly in regards to the vaulted arch roof. The reservoir has played a continuous, on-going role for over a century as an important facility of the water supply system, particularly for the eastern suburbs. The exterior of the reservoir has aesthetic qualities which relate to its parkland environment and is a local landmark. The level of ornamentation evident in the structure demonstrates the importance placed upon the appearance of engineering structures in the era in which it was built. The Centennial Park group of three reservoirs, including Woollahra Reservoir (WS 144), 1880, Centennial Park No.1 (WS 22), 1899, and Centennial Park No.2 (WS 23), 1925, demonstrate the development in construction technology for covered reservoirs, as well as the dramatic increase in demand in the growing Sydney suburbs. The group is unique in the Sydney Water system, because of their size, design and level of architectural detailing