1. Sodium level in the softened water.
When water is softened the elements that cause the hardness – calcium and magnesium ions – are exchanged for sodium ions. So the sodium content of the water increases. The Drinking Water Regulations set a limit of 200 milligrams per litre (mg/l) for sodium.
In most areas of the UK, the increase in sodium stays within this limit but in some very hard water areas the increase in sodium may breach the statutory limit laid down by these regulations. Whilst this may be of no significance to the majority of the population, it may be unsuitable for certain sectors of the population.
2. Hardness level.
When water is softened all the hardness minerals are removed. The current Drinking Water Regulations do not contain requirements for a minimum level of hardness but there are some studies which have demonstrated that presence of these hardness minerals may have some health benefit.
Because naturally soft water sources (lakes, rivers, etc) are often low in pH (slightly acidic), they can be corrosive to metals. Hard water that has been softened has been incorrectly assumed to suffer the same disadvantage. Softening water with a salt-regenerated, ion-exchange softener does not change the chemical properties that affect water corrosivity.
This erroneous concern has been extended to lead pipework (normally not present in modern buildings) but again, softening will not affect the corrosivity of the water towards lead.
The Drinking Water Regulations 2000 have introduced tighter standards for lead. Should you have concerns over the presence of lead pipework within your premises, you should contact your water company for further advice.
A domestic water softener should be kept in continuous use and maintained correctly. Whilst there is little to go wrong with a domestic softener and it will normally “fail safe”, long periods of stagnation of water within the softener (after extended holidays for example), may affect the quality of the water until it is flushed and returned to normal service again. Although not a health risk, the aesthetic quality (taste and odour) of the drinking water may be impaired.