Water as the medium for photochemical synthesis may, at present, be an unusual choice. This unique solvent offers more than being environmentally friendly: it can lead to increased or different reactivity and selectivity compared to organic solvents. Although water is perceived as a benign and green solvent, 1) it is often neglected when developing synthetic methodologies, in particular those based on photochemistry. More common are solvents such as dichloromethane (DCM) or acetonitrile (MeCN). However, water is not only an environmentally friendly but a unique solvent: for example, water contains little dissolved oxygen. 2) Being a triplet q...