Leeghwater was born as Jan Adriaanszoon. Only later did he adopt the name Leeghwater, from laag water or low water. It is not clear exactly how the prevalent spelling of Leeghwater’s name came about. Leeghwater himself spelt his name alternatively as Leegwater, Leegh-water, Leeghwater and Leechwater. He was born and living in De Rijp in a house on the opposite of the old townhall. Official documents of the time also mention Laechwater and Laachwater. Leeghwater, as a hydraulic engineer, was pivotal to land reclamation programs along the flooded coast of the Netherlands. 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 1607 and Leeghwater supervised the milling. Between 1607 and 1635, the polders Purmer, Schermer and Heerhugowaard were also created under his supervision. He was also known for bell casting and clock making in the church towers in Amsterdam.
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, it was with three large steam-driven pumping installations; one at Lijnden, Kaag, and Cruquius. The installation at Kaag, the Gemaal De Leeghwater, built with a steam engine in 1845 to pump water into the Kaag lake, was named after him. The other two men honored in this way were Frans Godard baron van Lynden van Hemmen, who wrote the 1821 book ‘Verhandeling over de droogmaking van het Haarlemmermeer’ with the 3-way steam pump reclamation plan, and Nicolaas Kruik, who wrote an early “water defence” plan in 1737 using windmills.