September 30, 2020

Where does the taste of tap water come from?

At school they teach that water has no color, smell or taste. And this is correct for “pure” water, but when we talk about the water that reaches our homes it is no longer so clear. The tap water in Madrid is famous for how much its inhabitants like it, and in other communities like Valencia it is usual to drink bottled water. Where does the taste of tap water and its differences come from?

It is difficult for us to find pure or distilled water in nature, it will always have a small concentration of other chemical compounds. The culprit is water itself, a magnificent solvent capable of wrapping a variety of chemical compounds with its molecules. If we leave a drop of distilled water outdoors, it will quickly absorb the different chemical compounds found in the air and on the ground.

For example, let’s think of a river that flows from the top of a mountain to its mouth in the sea. When the ice melts from the top, we will get a fairly pure and tasteless water, but as the river descends it will accumulate waste.

Today, a significant proportion of these wastes are generated by man, such as pesticide residues from nearby crops or chemical wastes from an industrial plant. But we also have other natural waste, such as water contacts with different animals that are going to drink to the river, living things that live in that water, and minerals from the river bed stones, eroded by the current.

As the river progresses, all waste accumulates in a unique proportion for each river and stretch of it. No two rivers are the same, and each river has its own chemical footprint influenced by its geography and nearby environment.

For this reason, rivers have always been problematic as a source of consumption. The only exception is mountain populations, in which the water remains purer. In the advanced stretches of the river, drinking its waters means exposing yourself to multiple dangers such as microorganisms that await your opportunity to reproduce in our body or man-generated contaminants. If we want to drink such water, we must filter it.

Improving the water that reaches us

We have been drinking filtered water for centuries thanks to the wells. The groundwater passes through different compressed layers of soil that leave behind any large particles that might be present, from branches to excreta remains. In this way, the water in the wells remains relatively clean and free of germs, unless it is contaminated from outside.

The human being has imitated this natural process through the process of purification of the treatment plants. In them, water circulates through several activated carbon filters, capable of absorbing and separating any large particles and some chemical compounds.

It is possible to add more filters and make the water even more pure, however from a certain point it is not viable. More filters means less water per second, and if we want to supply the faucets of the entire population we must leave some remains, always making sure that the water is drinkable and its consumption does not cause diseases.

In this way it is prioritized to obtain drinking water for large populations, in exchange for a more variable flavor. Sometimes the combination will be better, and sometimes worse. It can also change over time, if the river suffers a large flood that attracts new minerals to its interior or if the active carbon filters change to more powerful ones.

In contrast, water bottling factories are strategically located in the mountains, where river water is cleaner and additional filters are applied to leave purer water than tap water. They can afford it since they have more time between lots and lots of bottles. In this way they ensure that the water is more tasteless and its taste can be liked by everyone.

Due to the limitations of public wastewater treatment plants, there is always a minimum risk that microorganisms such as viruses or bacteria have managed to remain in the water, or that there is some contamination in the following pipes. To avoid health problems, tap water includes a small amount of chlorine, small enough not to affect the taste but just enough to prevent the growth of undesirable pathogens. In some countries such as the United States, water also includes iodine, which combines the antibacterial effect with oral protection. However, its frequent consumption has some side effects and in Europe almost no country adds it, Spain even.

In short, the water that comes out of our tap is not just water, but carries a variety of chemical compounds. The majority are carbonates and sulfates, coming from the land under the river, in addition to the chlorine itself that we add. Every time we drink a glass of tap water, we savor part of our geography and fauna. If you don’t like water, shout at the mountains.


  • There are minimum requirements for water to be considered potable, and all treatment plants have periodic quality controls to ensure that they meet these requirements. This means that even if chlorine is added or the remains of other compounds are left, they are in a proportion that does not affect health (but does taste).



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