If the average person needs 100 tons of water a year, and there are 10 billion people, that would be 1 trillion tons of water a year, or about 1000 cubic kilometers. There are 1,338,000,000 cubic kilometers, so that would increase salinization by one millionth every year... OR WOULD IT???
None of the normal uses of water destroy it. We dirty the water, but we do not destroy the water. The used water either becomes sewerage, or evaporates. Either way, it ends up back in the ocean, so the volume of the ocean should not change.
The only thing I can think of that destroys water is turning it into hydrogen. That is exceedingly rare these days, but may become more common in the future. The reason one would create hydrogen is as a partible energy source, and it would be recombined with oxygen to create water. In theory, that would mean the same amount of water, but it is possible there could be some lossage in that process. Who can tell, it is the future.