Johnston, William (c.1680s–1754), landowner and waterworks designer, was probably born in Scotland some time in the late seventeenth century, son of John Johnston of Scotland, who left his native soil soon after the Glencoe massacre (1692). Little is known of Johnston's life, but at an early age he acquired two estates on the outskirts of Belfast: the first was Newtownbreda, Co. Down, and the second in Newforge, Co. Antrim. In 1733 he sold the former to Arthur Hill-Trevor (qv) and used the profits to purchase a forty-one-year lease for the Belfast waterworks from the 4th earl of Barrymore (qv), trustee of the simple-minded 4th earl of Donegall, at a rate of 21s. a year. By this time, although his birth date is unknown, Johnston was presumably quite mature, for he apparently wanted to move to Belfast to ensure the proper education of his ten children. ‘Pipe Water Johnston’, as he soon became known, immediately set about modernising the water works by drawing up elaborate plans, including more branches, extending the supply to a greater number of houses, and bringing water into town from the Malone and Cromack districts through wooden pipes. Unfortunately, the scheme was never a success, nor did it ever make a profit for Johnston; by 1753 he was offering his lease to anyone who would take it for a minimum of seven years. The quality of the supply was said to have been so bad that by the time James Hall acquired the lease (1762) water was being carted in from adjoining towns. In recognition of the money Johnston lost through the venture, the Donegall family gave his son, also William (d. 1771), a gratuitous lease of land in Old Forge, near Belfast (1755).
Johnston additionally served as collector of Coleraine, and he died in October 1754. He was twice married, and had ten children with his first wife, Jane. His son William served in the navy and another, Mussenden, was a major in the army. One of his daughters married the Rev. William Saurin, rector of Belfast, and another married the Rev. Robert Heyland, rector of Coleraine. His grandson John Johnston (qv) became a fur trader in Canada. William Saurin (qv) was also a grandson. Late in life Johnston travelled to Liverpool, where he met and married his second wife, a widow; they returned to Ireland where he died several years after their marriage.