I imagine a lot of the freshwater savings involves not needing to feed an animal. What they drink and eat takes large scale agriculture and processing operations which will be cut drastically.
But you have to feed the cells. And you can't just grow some plants and feed it to the cells, you have to manufacture a very precise blend of chemicals (amino acids, sugars, surfactants, antioxidants, etc.) at >99% purity for each one. Often extremely nasty solvents are involved in the production process. Usually, some sort of petroleum product is a feedstock. Those chemically synthesized materials are hardly green.