Natural water may contain suspended matter, mineral salts and dissolved organic matter. Microorganisms are also part of the suspended matter.

The first condition necessary for the quality of a drinking water is the absence of microorganisms. Since they are associated as suspended matter, filtration is an essential water treatment, since apart from eliminating the turbidity that gives an earthy taste, it greatly facilitates disinfection. For this reason, in many places where there is poor water quality in developing countries, filters, even manual, are recommended as the most efficient measure.

Disinfection is completed by the use of chlorine. It is necessary not to confuse the chlorine element, which is actually dosed as sodium hypochlorite, with the chloride anion, one of the elements responsible for the salinity of water and an ion that is not harmful to health.

As for hypochlorite, it is not irritating at the doses used, -less than one part per million-, so its only effect is the slight taste that can be perceived, especially when the dose is close to 1 part per million and it is summer, when a gas is more easily released from the liquid in which it is dissolved. On the other hand, one must be aware that chlorine protects against infectious diseases that have been a scourge throughout history, such as cholera, which caused countless deaths, especially among children.

As a result, the microbiological quality of water in Spain is very high. Only in rare cases is the age of the distribution network so high that the presence of suspended matter can be suspected. And only in cases of pipe branches with water that has been standing for a long time can there be some accumulation of biofilm. In these rare cases, it is recommended to let the water run before use.

As for mineral salts, those found in natural waters do not have a significant effect on health. In any water, they are in small quantities. There are more salts in foods. If anything, the presence of bicarbonates may have a slight digestive effect by neutralizing the possible excess of stomach acid after a digestion with acidity, but the effect is very small. As for the hardness, that is to say, calcium, it can have in some cases a certain favoring effect on kidney stones, but on the contrary it can favor the strengthening of the bones. Therefore, in people of normal health, its overall effect is not very influential on health. Its only real effect is to give a certain metallic taste to the water, which is perceived by people accustomed to low mineralized waters.

Other ions, such as sulfate or magnesium, have even less influence, even though, in the 19th century, with the fashion of thermalism, various properties were attributed to them, and trace elements such as selenium or zinc, their presence is testimonial and their promotion is exclusively due to commercial interests.

As for dissolved organic matter, urban waters in towns of a certain size are filtered by activated carbon, which adsorbs both natural and artificial organic molecules, which in any case are found in low concentrations.

Therefore, mineral waters are in no way worthwhile for their supposed beneficial effects on health, whether they are low mineralized or highly mineralized. As we have said, only in particular cases, such as water for babies, may they be of some interest. The rest is marketing for a very lucrative industry. A very high price is paid for something that is almost free from the tap. It should be borne in mind that the plastic in the bottles can also transfer certain compounds, such as phthalates.

In any case, contamination by discarded water containers is enormously harmful, since recycling is very scarce and costly. The low efficiency of recycling and its conscience-soothing effect on what is really desirable, which would be to reduce the consumption of containers, deserve a separate chapter. Mineral water is a devastating example of the influence of the marketing of the consumer society, which has managed to clothe it with an attractiveness that has no basis in fact and a high environmental cost.