Nappy Leaks: Hard Water Made Easy

I like hard water. I love the way those little cubes cheerfully jostle and clink in my glass of G&T. I like them so much I’m always sure to drain my G&T nice and quickly before my hard water turns all runny again… Wait, you don’t mean THAT kind of hard water? Oh alright then. Let’s talk about dissolved minerals in your tap water and what they mean for your nappy wash.

To help get the facts right for this article, I’ve been talking to Mark Smith, our friendly scientific adviser who is a specialist in the chemistry of water and cleaning products.

Hard water is what we call it when our mains water supply contains a lot of dissolved minerals. It happens when water passes through rocks and dissolves a little of them as it goes. As they are dissolved, salts from the rock separate into smaller particles with a positive or negative charge: these are ions. In the UK we’re mostly concerned with calcium and magnesium ions. When you try to wash things in hard water you find that detergent and soap don’t foam so well and it’s harder to get things clean. Let’s find out a little more.

Why Hard Water Is A Problem

Calcium (Ca) and magnesium (Mg) ions in hard water ‘steal’ away cleaning power. These particular ions have a positive charge. Almost like magnets, they are attracted to the negatively charged anionic surfactants in your detergent and react readily with them, ‘stealing’ them away before they get to do their real job of grabbing hold of dirt so it can be rinsed down the drain. These surfactants are there to clean and we need them to do their job. They also make bubbles so that’s why we find hard water doesn’t foam so easily.

How To Solve The Problem

Use the right amount of detergent. Laundry detergent formulas include ingredients to deal with the hard water. Your detergent’s instructions will tell you how much to use if your water is hard, medium or soft and you can find out how hard your water is by looking at your water supplier’s website. The harder your water the more you’ll need to use (though soft water needs its fair share too) to make sure you get enough of the stuff that deals with those pesky ions.

How Does It All Work?

Modern detergents contain some very clever ingredients, usually called stabilisers or builders, which round up the Ca and Mg ions and shepherd them away so the detergent can do its job of cleaning. There are different ways to achieve this but they have to first attract the Ca and Mg ions (zeolites are a popular modern choice for this), and then make sure they stay dissolved in the water and don’t either react all over again with other things or turn into solid particles which could get left behind on the fabric (polycarboxylates are often used along with zeolites for this).

An alternative to using the high dose of detergent is to use a separate hard water treatment, such as Calgon, along with the soft water dose of detergent. The separate treatment works in the same way and effectively gives you soft water. You can then use less detergent. This might be useful if you dislike too much fragrance, if you are getting excessive amounts of foam, or if it’s physically difficult to fit the full amount of powder into your machine’s drawer. There are unbranded alternatives to Calgon but they don’t always contain the same ingredients (look for zeolites and polycarboxylates).

What About Soda Crystals?

Soda crystals or washing soda are names for sodium carbonate. It’s cheap and readily available and some sources say you can use it as a budget alternative to water softeners. Sodium carbonate alone does not do quite the same job as the more complex systems found in modern detergent and softener formulas. Washing soda works well at ‘capturing’ the Ca and Mg ions by forming calcium carbonate or magnesium carbonate. However those two compounds are insoluble precipitates: they become tiny solid particles which can’t dissolve again. That means you could have a chalky sort of dust floating around in the wash. It’s not clear how problematic that would be.

What If I Don’t Bother?

If there is not enough water treatment agent in the wash (either from your detergent or an added softener) then your washing water will have more calcium and magnesium ions in it.

Because those ions hijack the anionic surfactant, one of the main cleaning ingredients in your detergent, your detergent won’t work as well as it should and you might not get your nappies clean.

And that could cause a right stink.

Kate O’Hara

You can read more about the Nappy Science Gang project and join in with the science on our Facebook page.

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