In Hong Kong, about 80% of residents flush their toilets with seawater, thanks to a separate water distribution system set up in the 1950s. The approach conserves the city’s scarce freshwater resources, and has also been adopted by smaller communities like the Marshall Islands. As coastal populations and water demand rise, this idea may become more attractive elsewhere, though some researchers have worried about the release of potentially toxic by-products to coastal areas from treating seawater with chlorination. To the contrary, a new study suggests that the practice not only helps conserve freshwater but also may protect wildlife in marine ecosystems (Environ. Sci. Technol. 2015, DOI: 10.1021/acs.est.5b03796)....I had no idea that Hong Kong residents flushed their toilets with seawater; makes a lot of sense.
Something like this would require massive infrastructure investment on the part of a municipality; I presume that inland cities could not bear the cost. It would be fascinating to know which cities on the east, west or southern coasts of the United States are actually close enough to a source of seawater to where this is a viable option.