You churn it with a large volume of sea water and then discharge it when the salinity is only acceptably above the natural amount. I believe France limits it to

You churn it with a large volume of sea water and then discharge it when the salinity is only acceptably above the natural amount. I believe France limits it to 10% above the natural salinity. e.g. take 3 gallons of sea water and extract 1 gallon of fresh water. You have 2 gallons of +50% salinity brine. Churn it with 8 gallons of seawater and you're back to +10% salinity. Wash it out into the ocean.