Ernest S. Prentice, eldest son of Judge Prentice, was educated at Clifton College, Bristol. He was trained as an engineer by Sir Joseph W. Bazalgette, engineer of the main drainage of London, and W. Stroudley, mechanical engineer of the Brighton Railway. From 1885 to 1903 he held the position of assistant engineer at the London County Council. In 1900 he married Jessie Tanner, and by 1908 they had two children.
Prentice came to South Africa in January 1903 and settled in Johannesburg. He practiced as consulting engineer (water and sewerage), while also holding the position of consulting sewerage and sanitary engineer to the government of the Transvaal Colony. In 1905 he was involved in the construction of septic tanks in Bryntirion, an exclusive new residential suburb for high officials in Pretoria. He was an associate member of the (British) Institution of Civil Engineers. By 1906 he was a member of the South African Association for the Advancement of Science. At the association's annual congress in 1904, held in Johannesburg, he read a paper on "The bacterial purification of sewage", which was published in the association's Report for that year (pp. 428-434). In his paper he reviewed recent advances in sewage disposal and pointed out that percolating bacterial beds were about to be installed at Bloemfontein. At the same meeting a related paper, on the septic tank method of sewage treatment, was read by J.C.S. Beynon*.