Not sure if the coroner's files would still be retained still (perhaps PRONI, Belfast) but incident was widely reported, not just in local papers-
Weekly Freeman's Journal (Dublin), 9 Aug.1924: ... fatality was reported on Monday from Saintfield, Co. Down, where a number of boy scouts are in camp. While bathing in pond Alexander Denholm. Hatfield street, Belfast, got into difficulties ... was drowned...
Ballymena Weekly Telegraph, 9 Aug.1924: ... sad affair the fact that the deceaseds mother passed away some time ago, leaving him and a sister. His father, Mr. Alexander Denholm, who belonged to Edinburgh, and had been residing for a number of years in Belfast, was in Blackpool at the time of the ...
Belfast Telegraph, 5 Aug.1924: ... to attend funeral of Alexander Denholm, late Assistant Scout master and ... to-morrow (Wednesday), at 2.30 p.m., from Hatfield Street.
Northern Whig, 5 Aug.1924: ...drowned at Saintfield), Alexander, the beloved son of Alexander Denholm. Funeral to-morrow (Wednesday), at 2.30 p.m., to Newtownbreda, from Hatfield Street. Friends please accept this intimation. Alexander Denholm, 35, Hatfield Street.
Belfast Telegraph, 3 Aug.1925: ... Alexander, who died on 3rd August 1924, and was interred in Newtownbreda Cemetary. Ever remembered by his Father and sister. ALEXANDER DENHOLM. 35 Hatfield Street.
Note: cause of death likely asphyxia