This page is a translation of the Italian version, which remains the reference text. The service is installed in Italy, in Lazio and Emilia-Romagna. Read the Italian original
Water purifier or water softener: the difference
They are not two versions of the same thing and you do not choose one instead of the other. A softener treats all the water in the house and works against limescale: it protects the boiler, the washing machine, the taps and the tiles. A purifier treats only the water you drink and is there to change its taste and composition.
Anyone with very hard water who also buys bottled water has two different problems, and sometimes the honest answer is that both are needed. Below is the difference set out plainly, and how to work out which one you need.
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The difference in one table
| Water softener | Reverse-osmosis purifier | |
|---|---|---|
| What it is for | removing limescale | changing the water you drink |
| Which water it treats | all the water in the house | only the water from one tap |
| Where it is installed | on the incoming mains | under the sink |
| What it removes | calcium and magnesium | most of the dissolved salts |
| Can you drink it? | yes, but higher in sodium | yes, and that is the point |
| Does it protect the boiler? | yes | no |
| Does it give sparkling water? | no | yes, with the carbonator |
The line that surprises people most is the fifth. An ion-exchange softener replaces calcium and magnesium with sodium: the water stays drinkable, but it comes out higher in sodium than it went in. That is why many domestic installations leave one tap unsoftened for drinking water.
Which one you need
You need a softener if…
- white marks appear on the taps and the shower screen within days;
- the boiler or the water heater is losing efficiency and the technician mentions limescale;
- the washing machine and the dishwasher need a lot of descaler;
- the water in your town is officially classed as hard or very hard.
You need a purifier if…
- you buy bottled water and want to stop carrying it;
- the tap water tastes of chlorine to you;
- sparkling water is drunk in the house;
- you want a dry residue lower than the mains water gives.
If you recognised yourself in both lists, that is not a contradiction: they are two different problems that often turn up together, especially where the water is hard.
Can they work together?
Yes, and it is a common set-up: the softener on the incoming mains for the whole house, the purifier under the sink for drinking water. A purifier works better downstream of a softener, because the membrane fouls more slowly with less hard water.
The cost adds up, though, and they are two systems with two sets of servicing. If there is budget for only one, the question to ask is which of the two problems weighs more in your day: the limescale on the taps, or the crates of water to carry.
A common mistake
«I'll put in a purifier and then I won't have limescale any more.» It does not work: a purifier treats a few litres a day at one tap, while the limescale comes from the hundreds of litres passing through the boiler, the washing machine and the shower.
The reverse holds too: a softener does not remove the taste of chlorine and does not lower the dry residue the way reverse osmosis does. They are different tools for different jobs, and a seller offering one to solve the other's problem is selling badly.
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Questions about purifiers and softeners
Can I drink softened water?
Yes, softened water stays drinkable. But an ion-exchange softener replaces calcium and magnesium with sodium, so the water comes out higher in sodium than it went in. That is why many installations leave one tap unsoftened for drinking water, and for advice about sodium in your diet the person to ask is your doctor.
Does a reverse-osmosis purifier remove limescale?
It removes most of the salts, calcium included, but only from the water passing through that tap: a few litres a day. The limescale in the boiler, the washing machine and the shower comes from all the other water, and a purifier does nothing about that.
Does the softener have to come before the purifier?
It is not required, but where the water is very hard it helps: the osmosis membrane fouls more slowly and lasts longer. It is a choice worth having assessed against the water in your own town.
Which costs more, a purifier or a softener?
They are of a similar order of magnitude to buy, with the softener additionally needing regenerating salt as a running cost. The comparison should be made over three or five years, servicing included, not on the price of the appliance.