Both reverse osmosis and activated carbon filters remove the bad stuff from the water. But each one works differently.
With a reverse osmosis filter, the water goes through a series of membranes. These membranes are designed to separate certain minerals and chemicals from the water.
Then, the purified water flows through the second set of membranes. This time, the membranes are designed to remove any remaining contaminants.
An activated carbon filter doesn't have these two sets of membranes. Instead, it uses carbon particles to absorb impurities.
Reverse osmosis systems are more expensive than activated carbon filters. However, they're also more effective.