Always a staunch Liberal, he objected to those Liberals who joined the coalition under David Lloyd George (see above) in 1918 though by 1933 he won the warm commendation of Lloyd George for unequivocally affirming that it was the duty of a Liberal to leave the Coalition Government. During World War II he actively supported the campaign for a Secretary of State for Wales and his proposal to that effect was unanimously passed at a conference of local authorities at Shrewsbury in June 1943.

Thomas Waterhouse was a good example of a person of wholly English stock who became rooted in Wales, which he then served skilfully and tirelessly. Since there was no English Wesleyan cause at Holywell, the family joined the English Congregationalist Church to which they gave substantial support. Trim and dignified, Thomas Waterhouse had a clear mind; he was tough yet fair, and those who knew him well realised that he also had a warm heart and a lively sense of humour. A fearless, independent man, he upheld for over half a century the highest standards in the public life of his county and country. He m. Doris Helena Gough, Olton, Warwickshire, in 1915; they had four sons and one daughter. He d. 3 July 1961. There is a portrait of him in Clwyd county council office at Mold, and another at the home of his son, Sir Ronald Waterhouse, High Court Judge.