Question

To be considered fresh water, water must contain salt in a concentration _____. more than 30 parts per thousand less than 0.5 parts per million less than 0.5 parts per thousand more than 40 parts per million

Answer 1

Some sources claim that the limit is 1 part per thousand or even 3 parts per thousand. According to the most accepted definition of fresh water, the dissolved salts have to be in a proportion of less than 500 parts per million. This means that the proportion has to be less than 500/1000 parts per thousand, hence less that 0.5 parts per thousand.