Are water conditioners worth it?

Chris Smith asked chemistry writer Philip Broadwith...

Phillip - Okay, well there's two things here. There's magnetic devices, which I think I can fairly safely say if they're outside of the pipes do next to nothing, they might wiggle, but you've got ions dissolved in the water. So you've got charged things moving, charged things that move, and have a magnetic field associated with them. So there is certainly probably some kind of interaction between the magnet and the ions moving. Whether that stops them furring up your pipes, I don't think that that's true. But, what I think Neil's talking about in this question is something called a water conditioner, which is slightly different to a water softener. So I'm just going to quickly go through what those two different things are. A water softener uses a kind of resin and it's the same kind of thing you might have in a jug in your kitchen or like plumbed into your house. What hard water is caused by minerals in the water, calcium carbonate, and it's the calcium particularly, that's the problem. If you take the calcium away, which is what the ion exchange resin in those filters does, and replace it with sodium, you end up with something that doesn't then form limescale. So that stops you from making a limescale. So that's a kind of chemical reaction. It's an exchange. You take the calcium away and you replace it with sodium. But the problem with that is you can't then really drink the water. It's got too much sodium in it. You become high blood pressure, because there's all sorts of other problems. So you have to have a separate water tap if you have a softener plug plumbed in.

Chris - It is quite funny to not tell people that if you have a guest over at your house and you see what the reaction is and see if they comment on the water and if they come from London and they've been drinking Thames tap water, then inevitably they often say actually the water tastes better. <laugh>

Phillip - <Laugh> Yeah. But what Neil, I think is talking about is something called the water conditioner, which is slightly different. It's the same kind of idea. We're going to change the chemistry of the water slightly to stop it making limescale. Instead of exchanging the ions, instead of taking the calcium out and putting sodium in, it puts into the main pipe something that has a block of zinc in it and some brass. And as the water flows through, it dissolves the zinc into the water. So you end up with zinc ions and that encourages the calcium to still form a scale. It still forms a solid, but it's a different form of calcium carbonate. When you do get lime scale, it's softer, so it doesn't kind of plate so much onto your kettle or your shower and it's easier to clean off.

Chris - So the pressure of movement through a pipe, for example, should dislodge it.

Phillip - Yeah, I mean, I haven't seen a lot of results like furring up in pipes. But one of the tests that they do with these things is take some of the water that's been treated, get an immersion heater, stick it in a bucket of water, run it for six hours at 75 degrees, and then dissolve off all the scale and see how much calcium is stuck to that immersion heater element. And if you take water that hasn't been treated and water that has been treated, the water that has been treated has about a quarter as much scale on the element after that test.

Chris - Thanks very much Phil.