https://phys.org/news/2019-01-toxic-brine-desalination.html

For every litre of freshwater output, however, desalination plants produce on average 1.5 litres of brine (though values vary dramatically, depending on the feedwater salinity and desalination technology used, and local conditions). Globally, plants now discharge 142 million cubic meters of hypersaline brine every day (a 50% increase on previous assessments).

That's enough in a year (51.8 billion cubic meters) to cover Florida under 30.5 cm (1 foot) of brine.