Ion exchange softening adds sodium in proportion to the hardness removed. For most people that is not significant, but the regulations require an unsoftened supply for drinking and food preparation, and it matters specifically for sodium-restricted diets and infant formula.
What softening actually changes
Ion exchange trades calcium and magnesium for sodium. The exchange is proportional: the more hardness removed, the more sodium goes in. So the sodium content of softened water depends directly on how hard the incoming water was.
In a soft water area, a softener adds very little sodium because there was very little hardness to remove. In a hard water area like this one, it adds more. That is the relevant fact, and it is why the guidance is framed around hardness rather than around softeners in general.
Why the hard tap is required
The Water Supply (Water Fittings) Regulations require that a supply of unsoftened water is retained for drinking and food preparation. In a domestic installation that is the kitchen cold tap, taken off the rising main before the softener.
Three distinct reasons sit behind it:
- Sodium intake. Most people’s dietary sodium comes overwhelmingly from food rather than water, and the contribution from softened water is small in that context. But it is not zero, and for anyone whose intake is medically restricted it is a real consideration.
- Infant formula. Formula is made up to a specific composition and the guidance is to use water that has not been softened. This one is worth taking seriously rather than treating as excessive caution.
- Other uses. Aquariums need specific water chemistry and softened water is not suitable. Some plants also do better on unsoftened water.
Anyone on a medically restricted sodium intake, and anyone making up infant formula. If either applies in your household, use the hard tap for those purposes and mention it to your GP or health visitor if you want specific advice. For everybody else, the hard tap exists as a sensible default rather than because softened water is harmful.
What about the taste?
People notice two things when they move to softened water, and neither is sodium.
- Soap feels different. Softened water does not strip soap the way hard water does, so it rinses differently and can feel slippery. That is the soap behaving normally rather than being stripped by calcium, and most people adapt within a week or two.
- Tea and coffee taste different. Dissolved minerals affect extraction, and people used to hard water sometimes prefer the taste of tea made with it. Since the drinking tap is hard anyway, this is easily resolved – use the hard tap for the kettle if you prefer.
Sodium at the levels involved is not detectable as saltiness. Water that tastes salty indicates a fault – most commonly a softener that has not rinsed properly after regeneration, which is worth investigating.
Practical arrangements
| Arrangement | How it works |
|---|---|
| Hard kitchen cold tap | Standard and simplest. The kitchen cold tap is taken off before the softener, so it is unsoftened for drinking and cooking |
| Hard tap plus a filter | The unsoftened supply also fed through a carbon filter, giving hard water that tastes better. A common and sensible combination |
| Separate drinking tap | A dedicated small tap on the worktop fed from the hard supply, leaving the main kitchen tap softened for washing up |
| Three-way tap | One tap delivering hot, softened cold and hard filtered cold. Neat, and more expensive to replace |
| Fridge and ice maker | Should be fed from the hard supply. Worth checking – it is frequently plumbed from whatever pipe was nearest |
The fridge point is worth emphasising. A plumbed fridge or ice maker is a drinking water outlet, and it is very often connected to whatever supply was convenient during a kitchen fit. If you have a softener, it is worth establishing which side of it your fridge is on.
See filtration, softening and conditioning for what a filter does and does not do.
Common misunderstandings
- ‘Softened water is full of salt.’ It contains sodium, not sodium chloride, and in proportion to the hardness removed. The salt used in regeneration goes to drain, not into your supply.
- ‘You cannot drink softened water at all.’ For most people it is not harmful. The hard tap is a regulatory requirement and a sensible default, particularly for specific groups.
- ‘A softener removes minerals you need.’ Calcium and magnesium in drinking water are a minor contributor to dietary intake compared with food. And the drinking tap is hard anyway.
- ‘Softened water is corrosive to pipes.’ Softened water is mildly aggressive towards existing scale, which is why it slowly dissolves deposits. It is not a corrosion problem in normal domestic plumbing.
- ‘The softener makes the water taste salty.’ It should not. If it does, the machine is not rinsing properly after regeneration and needs looking at.
Fitting a softener? Make sure the fridge, the ice maker and any drinking tap are on the hard side. It is easy to get right at installation and awkward afterwards.
Questions we get asked about this
Is softened water safe to drink?
For most people it is not harmful, but the regulations require an unsoftened tap for drinking and food preparation and that is what should be fitted. It matters specifically for sodium-restricted diets and for making up infant formula.
How much sodium does softening add?
In proportion to the hardness removed – harder incoming water means more sodium in the softened output. In a hard water area the addition is more than in a soft one, which is why the guidance exists.
Can I use softened water for baby formula?
The guidance is to use unsoftened water. That is what the hard tap is for, and it is worth being deliberate about it.
Why does softened water feel slippery?
Because soap is not being stripped by calcium and therefore rinses as it is designed to. It is the soap behaving normally. Most people get used to it quickly and many prefer it.
Should my fridge be on softened or hard water?
Hard – it is a drinking water outlet. Plumbed fridges and ice makers are very often connected to whatever pipe was nearest during a kitchen fit, so it is worth checking.
My softened water tastes salty. Is that normal?
No. Sodium at the levels involved is not detectable as saltiness. A salty taste suggests the machine is not rinsing properly after regeneration, and it needs looking at.
Regulations and standards referenced on this page
- The Water Supply (Water Fittings) Regulations 1999 (SI 1999/1148) — UK Statute Law Database
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