Frederick Graff (27 August 1775 – 13 April 1847) was an American hydraulic engineer who designed and built the Fairmount Water Works in Philadelphia, Pennsylvania, and unofficially invented the fire hydrant.

On 1 April 1805, he was elected superintendent and engineer of the works, but they were determined to be inadequate after several years of usage.

In 1828 he received another award from the water committee “as a testimonial of respect for his talents and zeal effectually displayed in overcoming unforeseen difficulties encountered in the construction of the northeast reservoir at Fairmount".

[3] His experience and ability became acknowledged throughout the country, and he supplied detailed information to aid in the development of 37 other waterworks in the United States, including those in New York City and Boston.

[6] He was engaged for 42 years in the service of the city of Philadelphia, and a monument to his memory was erected on the grounds of the Fairmount Water Works.