Cleaning tableware and cookware after eating. About a tenth of household water goes here, and all of it has to be potable: French rules permit rainwater indoors for flushing, floor washing and laundry, and not for dishes. The choice is between an appliance and a sink, and unusually for this catalogue the appliance wins on water by a wide margin, because a machine reuses its wash water through a cycle while a tap throws every litre away once.
Ranked by water used per item cleaned, which is the axis the evidence actually measures and the one that binds in a house on a tank. Energy is a second axis and runs the same way here, since most of the energy in dishwashing is spent heating water. Hand washing is not one technique but a spread: the same study that puts the average at about 100 litres a load records 33 at best and 440 at worst, and the difference is entirely whether the tap runs.