Slight clarification - osmosis involves a membrane which allows water molecules to go through while blocking dissolved mineral ions. Reverse osmosis requires pressure to force the water molcules through, as it is the reverse path from conventional osmosis.
In conventional osmosis, water moves across the membrane from a higher concentration of water to a lower concentration of water (example: FW on one side, SW on the other - water moves from the FW side to the SW side in increase the water concentration on the SW side, eventually it will equalize the two).
In RO, we are forcing water to move from the lower concentration of water (i.e., water + minerals to water with fewer minerals), so it is the reverse of normal. We are increasing the water concentration by the use of pressure.
HTH