Jan Adriaanszoon Leeghwater (De Rijp, The Netherlands) was a Dutch mill builder and hydraulic engineer. He was involved in the reclamation of the Beemster polder, the first polder in the world created from a lake by draining the water using wind mills. The reclamation of the Beemster was started in in 1607 and Leeghwater supervised the milling. Between 1607 and 1635, the polders Purmer, Schermer and Heerhugowaard were also created under is supervision.
Leeghwater was among the first to advocate reclamation of the Haarlemmermeer, a lake whose growth presented a danger to the surrounding towns (several villages were swallowed and even Amsterdam and Leiden were eventually threatened). When this was finally accomplished in 1852, one of the three large pumping installations was named after him. This installation, the Leeghwater-gemaal, is still in use today.
It is not clear exactly how the prevalent spelling of Leeghwater's name came about. Leeghwater himself spelt his name as Leegwater. A curious fact about the name Leeghwater which may be of interest to non-Dutch speakers, is that it translates literally to empty water.