Does a Water Softener Affect Drinking Water Safety?

The sodium content of softened water depends directly on the original hardness. The higher the hardness minerals removed, the more sodium replaces them. As a rough guide:

• Soft water area (100 ppm hardness): softening adds approximately 4mg of sodium per 240ml glass
• Moderately hard (200 ppm): approximately 8mg per 240ml glass
• Very hard (400 ppm): approximately 15mg per 240ml glass

For context, a slice of bread contains around 150 to 200mg of sodium. The amount added by drinking softened water is genuinely small relative to normal dietary sodium intake.

The UK Drinking Water Inspectorate (DWI) and most NHS guidance state that softened water is safe for healthy adults to drink. The sodium levels resulting from domestic water softening fall well within acceptable safety limits for people without specific dietary restrictions.

The World Health Organisation recommends that drinking water sodium should ideally not exceed 200mg per litre. Even in very hard water areas, sodium from a correctly operating domestic softener stays well below this threshold in the softened output water.

Two groups where softened water for drinking merits more thought:

• People on a medically supervised low-sodium diet: If a GP or consultant has specifically advised limiting sodium intake due to heart disease, kidney disease, or hypertension, the additional sodium from softened water is worth discussing with them. Most will advise using an unsoftened tap for drinking and cooking.
• Babies and formula: NHS guidance recommends that water used to make up infant formula should not be softened. The sodium levels, while safe for adults, are too high for young infants whose kidneys cannot process excess sodium effectively. This applies until babies are established on solid food and drinking ordinary water.

The practical answer most UK households adopt is straightforward: leave one cold kitchen tap connected to the unsoftened rising main. This tap — usually the main cold kitchen tap — delivers hard water directly from the supply for drinking and cooking. The rest of the house runs on softened water for all other purposes.

This configuration is standard practice in the UK and is built into most water softener installations as a matter of course. It costs nothing extra and requires a simple bypass in the installation pipework. If you are getting quotes, confirm this will be included — any reputable installer will do it automatically.

Many people notice a slight difference in the taste of softened water — often described as slightly flatter or silkier than hard water. Some prefer it; others prefer the mineral taste of hard water. Neither perception is wrong.

If you find softened water tastes of chlorine or has any off-note, that is not from the softening process — it is from the mains supply itself. An under-sink activated carbon filter on the drinking tap (which can be the unsoftened tap) addresses chlorine taste effectively at low cost.