UK Official Development Assistance (ODA) spend is recorded in line with the Organisation for Economic Cooperation and Development's Development Assistance Committee coding. This does not specifically record water resilience. Yearly UK bilateral ODA spend on water and sanitation, including water resilience, can be found in the respective Annual Statistics on International Development publications: https://www.gov.uk/government/collections/statistics-on-international-development.
Following the recent spending review and autumn budget, the Foreign, Commonwealth and Development Office has started the process of allocating sectoral funding. This process should provide some more clarity on sector specific funding over the coming months.