Abstract Mining is usually associated with draining of large quantities of water. On the other hand, mining operations themselves are water users for purposes like coal or ore washing, dust mitigation, recultivation, etc. The normally existing water surplus can be seen as a resource for public purposes instead of discharging the water to rivers and the sea. It is typical for the mining operation that these water amounts vary spatio-temporally according to the mining process. The R&D project WaterMiner investigates the example of the Hon Gai hard coal mining area in Ha Long, Vietnam, as to how and to what extent under the variable spatio-temporal conditions the mine water can cover the water demand in the mines themselves and contribute to the public water supply in the surrounding settlement area of Hon Gai. The spatio-temporal change of mine water drainage, mine water treatment and mine-internal water use and the potential mine-external water use volumes in the project region are investigated by a material flow model and visualized by Sankey diagrams, maps, and tables. Several options for delivery of mine water for mine-external water uses as a contribution to the public water supply are shown.