The difference between a water purifier and an osmosis unit is mainly in the size and type of filtered elements. For example, a purifier only uses filters, such as activated carbon, which will not filter out the smallest particles and molecules. This is what we find in particular in portable filtration systems, such as filters for carafes, and bottles or to be fixed directly on the tap.
In addition to the use of filters, osmosis filtration has [reverse osmosis technology](https://www.simpurelife.com/collections/reverse-osmosis-systems). It retains pesticides, nitrates, drug residues (anti-inflammatories, etc.), and heavy metals such as lead, aluminum, copper, chromium, or arsenic.