The sense of taste and smell is perceived by various receptors in the mouth, throat and nasal cavity. When we eat and drink these sensations are perceived jointly. The volatile compounds move from the mouth to the sensitive part of the nose causing the sensation of smell. At the same time the receptors located in the mouth perceive the sensations which are the combination of smell and taste as well.
The inorganic ions located in the water are odorless except for the ammonium ions and sulfides. In certain circumstances, however, they affect the water taste. The number of the inorganic ions in saliva has an impact on water taste. If the amount of these substances is approximate to what our receptors are adapted to, then the drunk water tastes better.
A Significant content difference between ions in consumed water and saliva might cause taste discomfort while drinking but this has nothing in common with water quality. Getting used to something is second nature for humans, therefore the improvement of the water quality by reducing various chemical compounds is considered by the users as a taste worsening which diverges from current habits.
Some metal ions which might be present in drinking water, can worsen the taste. One of them is iron, its limit of permissible concentration is 0,2 mg/dm3, whereas by 0,05 mg/dm3 the taste is getting worse. Additionally, some organic compounds that are in the water in ultra-low concentrations do not affect the health badly but can cause the effect of worse taste and smell of the water. For instance, the organic compound 2,3,6-trichloroanisol is smelt by 0,1 ng/dm3 (0,0000000001 g in 1 liter).
Even high-tech measuring devices do not have such a detection limit. And low concentrations that cause water to smell worse are totally harmless for the health. The similar examples can be easily found. Water complaints are often associated with chlorine smell. However that smell can be readily neutralized by the water boiling and its presence guarantees full bacteriological safety. It also signifies that the time of the water flow in the waterwork wire from the water treatment plant to the customer (time of water stopping) is not too long, so it eliminates water pollution after effect. The amounts of the chlorine or chlorine dioxide used for water treatment are harmless for the health.