Garstin was Under Secretary of State for Public Works in Egypt. He held this position during the construction of the Aswan Low Dam across the Nile 1898–1902. For his services to this project he was appointed a Knight Grand Cross of the Order of St Michael and St George (GCMG) in December 1902. In early 1903 Garstein and a surveyor travelled the Lake Edward, the Semliki River and the Lake Albert, and visited Mombasa, Uganda, Gondokoro and Khartoum.
After his death Garstin was cremated at Golders Green Crematorium.
The extinct giant snake Gigantophis garstini was named in his honour.
- "Garstin, Sir William Edmund (1849–1925), civil engineer". Oxford Dictionary of National Biography. doi:10.1093/ref:odnb/33342. Retrieved 23 April 2022.
- "No. 27503". The London Gazette. 12 December 1902. p. 8589.
- "Latest Intelligence - Sir W. Garstin". The Times. No. 36959. London. 24 December 1902. p. 3.