In 1782, the 3rd Earl of Egremont of Petworth House installed the Beam Pump alongside the watermill to provide more water for the town of Petworth. Before then, water had been supplied by springs and conduits as well as private wells.
The Beam Pump was powered by a waterwheel, and pumped river water for 1½ miles (2.4 km) to Petworth through a cast iron pipe, 3 in (7.6 cm) diameter. The water was stored two cisterns; one on Lawn Hill for Petworth House, and the other in Grove Street to serve the town. The first water wheel was wooden and undershot. This was replaced in 1858 by the present more efficient breastshot iron wheel.
The Beam Pump was capable of delivering up to 20,000 gallons (91 litres) of water a day to Petworth – it was likely to have been operated twice a week to fill the cisterns. Although no doubt the river water was drunk on occasion, it was not intended for human consumption.
In 1839, as well as Petworth House, the Beam Pump was supplying water to 7 public stopcocks and 137 private taps owned by 69 people in the town.
The Beam Pump survived after the last mill building was demolished in1973. The water from the pump has now been diverted to the fountain just outside the Pump House.