Reverse osmosis (RO) works by filtering the tap water indoors through a membrane. You can compare it with the root of a plant: it absorbs water but keeps dirt out. For the membrane at home, this means a system that lets water molecules through, but not most dissolved and suspended substances.
The osmosis unit is placed between the water pipes and removes up to 99% of the limescale from tap water, as well as most other dissolved substances (ionic or mineral salts). Pharmaceutical residues, hormones, heavy metals, organic compounds, bacteria and viruses are also removed. Only the very smallest ions (such as fluoride) are barely held back — they are so small that they fit through the micropores of the membrane. This also depends on which membrane is used.
Commercial suppliers use membranes of about 0.1 micron for households. Large production companies, which use water for production processes, filter much further — down to as little as 0.0001 (ultrafiltration). At that point you no longer speak of microns but of kilodaltons (KD). H2Ot's systems only use the professional variant, with a filtration of 0.002 KD. This means 99.999999999% of substances are held back.
Most suppliers of water softeners and water systems don't use these kinds of professional membranes, but combine a membrane with a filter — often a carbon filter and/or sediment filter. An osmosis unit can also be followed by an additional ion exchanger and/or UV filter for slightly better purification.
In most places in the Netherlands, RO is not needed at home: there, ultrafiltration is the better choice. But where the water is brackish or salty, such as on the Wadden Islands or in other remote locations, and in countries with brackish or salt water, RO is exactly the right solution for the home.
Even so, we also offer an RO solution ourselves: our reverse osmosis systems are combined with a remineralisation step, which adds back the minerals the RO process removes from the water. That way you still get balanced, drinkable water — a combination few other suppliers offer.