low volume water vapor
The idea is to use water under high pressure. Similarly as in the washer machine. Faucet with a aera

Solution

In public buildings the most frequent use of water is for hand washing and for flushing. The problem of washing hands can be handled the following way. Instead of the usual running tap water used for hand washing we can use steam. Similar systems are used in hand carwash. In Carwash steam is fed under high pressure by a compressor. I suggest using a pressure in a water system and aerator mixer with micro-holes to create steam. This will significantly reduce water use. Aerators can be replaced on already existing mixers, which would minimize the cost of transformation.