Francis Edgar Kanthack, civil engineer, was a son of Emilio Kanthack and his wife Johanna Victoria Zimmer, who had settled in England from Germany. He received his schooling at Liverpool College and from 1885 to 1890 in Lueneburg, Germany. Upon his return to England he entered the Royal Indian Engineering College at Cooper's Hill, near London, in 1891 and graduated in 1894. After completing an apprenticeship at the Cardiff waterworks he was appointed in 1895 as assistant engineer in the Indian Public Works Department, stationed in the Punjab. There he gained wide experience of irrigation work during the next eleven years. In due course he became a member of both the (British) Institution of Civil Engineers and the Institution of Mechanical Engineers. In July 1899 he married Rosa Higham, daughter of the inspector-general of irrigation to the Indian government. They eventually had one son and two daughters.
In 1906 Kanthack was granted leave of absence for two years and allowed to take up a two year contract appointment as hydraulic and irrigation engineer to the government of the Cape Colony. He arrived at the Cape in October that year. In 1908 he resigned from the Indian civil service and was appointed director of the Department of Irrigation of the Cape Colony. He became a member of the Meteorological Commission of the Cape of Good Hope that same year. Immediately after his appointment he began a vigorous survey of the water resources of the Cape and established a network of gauging and rainfall stations. The work done by his department was reported in the annual Report of the Director of Irrigation..., while he also wrote several pamphlets and reports, as well as the following articles in the Agricultural Journal of the Cape of Good Hope: "The economical use of water in irrigation and the measurement of stream and furrow discharges" (1907), "Sluits [dongas], their evil and prevention" (1907), "The destruction of mountain vegetation: its effects upon the agricultural conditions in the valleys" (1908), "Irrigation development in the Cape Colony" (1909), and "[British] Bechuanaland from the irrigation standpoint" (1909, in 4 parts). At the First South African Irrigation Congress in 1909 he delivered a paper on "Irrigation development in the Cape Colony: Past, present and future", which was published in the Proceedings. He became a member of the Cape Society of Civil Engineers, serving on its council in 1910, and contributed a paper on "The design of irrigation channels to prevent silting and scouring" to its Minutes of Proceedings (1909, Vol. 7).
After the formation of the Union of South Africa in 1910 Kanthack became director of irrigation for the Union. Under his guidance the hydrographical and meteorological activities of the four provinces were amalgamated in the Union's first meteorological service in 1912. He played an important part in the drafting of the Irrigation and Water Conservation Act of 1912 and directed the development of, among others, the Sundays River, Olifants River, Kammanassie, and Hartebeespoort irrigation schemes. In the course of this work he travelled all over South Africa and built up an unrivalled knowledge of its water resources. During World War I (1914-1918) he served as a civilian in the forces of General Louis Botha during the campaign in German South West Africa (now Namibia) and rendered invaluable services in connection with water supplies in that territory and elsewhere in Africa. For this work he was appointed by the British government as a Companion of the Order of St Michael and St George (CMG) in 1917.
After the war he led the South African delegation to negotiations regarding the border between South West Africa and Angola and in 1920 signed a provisional agreement with the Portuguese delegation on the banks of the Kunene River. He used the opportunity to study the river and described it in his "Notes on the Kunene River, southern Angola" (Geographical Journal, London, 1921). During a visit to England in 1919 he wrote a short memorandum, aimed at British settlers, on Irrigation and land settlement in the Union of South Africa (London, 1919, 16p). In 1920 he compiled a report on "The water power of the Union of South Africa", which was published in installments in the South African Journal of Industries. The report was partly based on the work of two engineers appointed by the Irrigation Department in 1917 and 1919 for a special investigation into water power. It included the first comprehensive assessment of available water in South Africa and an analysis of possible water power schemes on 48 South African rivers. In 1922 he published a paper on "Irrigation in South Africa" in the South African Geographical Journal (Vol. 5, pp. 13-24). That same year he joined the Department of Civil Engineering of the University of Cape Town on a part-time basis as a reader in irrigation and water supply. Two years later he published The principles of irrigation engineering with special reference to South Africa (London, 1924, 299p), based on the lectures he delivered at the university.
In 1920 Kanthack resigned his post and on 1 April 1921 started in private practice as a consulting engineer in Johannesburg. During the nineteen-twenties he explored the rivers of Northern Rhodesia (now Zambia) to assess their hydro-electrical potential for Broken Hill (now Kabwe) and the copper mines. He, and later the firm F.E. Kanthack and Partners, acted as consultants for hydro-electric projects considered or initiated by the South African Railways and Harbours, the Victoria Falls and Transvaal Power Company, the Anglo-American Corporation, and the Electricity Supply Commission. He was also involved in the civil engineering works of most of the large thermal power stations built in southern Africa during his time, and in the erection of the steelworks of the South African Iron and Steel Corporation (ISCOR). Some of the firm's work was carried out in other African countries, namely present Zimbabwe, Zambia, Tanzania and Malawi, and written up in several reports. For example, he wrote two papers on the fluctuations (1941) and hydrology (1942) of Lake Malawi, as well as a Report on the measures to be taken to permanently stabilize the water level of Lake Nyassa (Lake Malawi; Zomba, 1948). On the basis of his extensive knowledge of rainfall statistics and water resources he wrote an article on "The alleged desiccation of South Africa" for the Geographical Journal (London, 1930). He retired in June 1958.
Kanthack served as president of the South African Society of Civil Engineers in 1913 and in 1954 was awarded the gold medal of its successor, the South African Institution of Civil Engineers, in recognition of his important contributions to the profession. He was president of the South African Institution of Engineers for 1938/9, president of the Associated Scientific and Technical Societies of South Africa in 1946, and at some time also president of the South African Geographical Society. In 1907, shortly after his arrival in the Cape Colony, he joined the South African Philosophical Society, remained a member when it became the Royal Society of South Africa in 1908, and was elected a Fellow of the latter in 1913. In 1907 he became a member also of the South African Association for the Advancement of Science, served on its council for some years, and was president of Section A in 1915. During the nineteen-thirties he was chairman of the Civil Engineering, Architectural and Building Committee of the South African Standards Institution. He became a member of the council of the University of the Witwatersrand in 1938, a position he held until 1959, and served as its chairman from 1954. The university awarded him the honorary degree Doctor of Science (DSc) in 1942 and after his death named the professorship in civil engineering after him. He was characterised by immense energy, endurance in the field, confidence in his own judgement, integrity and a high sense of duty, but also by an autocratic attitude and intolerance of mediocrity. He was widely read and had a strong interest in archaeology and natural history.