Ordinary osmosis cannot be used to purify water. If the applied pressure exceeds osmotic pressure then water starts moving from solution side to pure solvent side. This is reverse osmosis, by which pure water is squeezed out of impure water.
Advantage: this process removes lead, calcium, magnesium, sodium, chloride, nitrate, sulphate, etc.
Disadvantages: it requires large volume of water. It may take as much as 90 gallons of water to recover 5 gallons of usable water.