Sir William Slingsby (29 January 1563 – 1634) was an English soldier who is often[1] erroneously noted as the discoverer of the first spa water well in Harrogate, North Yorkshire.

[2] After marrying Elizabeth Broard, daughter of Sir Stephen Broad of Broadshill, Sussex, in 1582, the couple took a Grand Tour of Europe, returning in 1594.

In 1596, Slingsby discovered that water from the Tewit Well mineral spring at Harrogate possessed properties similar to that from Spa, Belgium.

He purchased the estate of Kippax, West Yorkshire, from Francis Bailden.

In 1601, he was made the junior Member of Parliament for Knaresborough alongside his brother, Sir Henry Slingsby, serving until 1611.