High throughput wide-field second harmonic imaging enables the label-free imaging of interfacial (< 3 nm thick) water, with a spatial resolution of similar to 370 nm using similar to 100 ms acquisition times per image. The obtained interfacial orientational order of water can be used to create spatiotemporal transmembrane potential maps of free-standing lipid membranes, giant unilamellar vesicles or living cells. These maps are then used to uniquely quantify membrane-water interactions, which show surprisingly heterogeneous behavior which sheds new light on processes such as ion transport, ion channel operation and membrane deformation.