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As I discussed in a previous blog, there may be biological, organic and inorganic substances in the water. In drinking water (tap water or mineral water) there should be no biological or organic substances. What separates water from water is the inorganic substances, the minerals. Some substances are present in large quantities, others in smaller quantities and others should be completely absent.


Fundamental for water properties, both as drinking water and for other household use, is its pH. Desirable pH for drinking water is about 5 to 6, slightly acidic. Historically, rainwater had this pH, but contamination of the air (with oxides of sulfur and nitrogen) has changed this so that rainwater today has pH between 3 and 4. This acidification is also the reason why rain destroys ancient marble statues and causes metal structures to rust away so fast.


Calcium and magnesium The substances present in large amounts in water (both tap water and mineral water) are salts, carbonates and bicarbonates, mainly calcium and magnesium. These salts make the water hard, which means that soap and detergents give sticky deposits (and require more laundry detergents), and also pans and coffee makers get lime deposits on the inside. The hardness of water varies greatly between the tap water at different places and between different mineral waters. Hardness is also noticeable on the taste of the water. Some classic mineral water is very hard with characteristic taste, the local Majorcan is a bit softer. If you want hard or soft water depends on the use. If you want the water to drink, it’s a matter of taste, some want the distinctive flavor of a hard mineral water, for example, from Marienbad or Vichy, others prefer mineral water with lower hardness. It is therefore not arbitrary which mineral water you choose.

Should you use the water to make coffee or tea you should use soft water because calcium and magnesium bicarbonate, which are slightly soluble in water, when boiling are converted to the corresponding insoluble carbonates. They fall out and lay as a coating on the inside of pans and brewers and furthermore destroy the taste of especially tea. The hardness in Spanish is called mineralización. For tea and coffee, you should choose “mineralización debil” or “mineralización muy debil”.

In many places in Majorca, the tap water is hard and gives coating already after a short time. To remove it from pots and brewers, boil water with a couple of teaspoons of citric acid and leave for an hour to dissolve the coatings. Citric acid forms complex with calcium and magnesium, is available at the pharmacy and is much cheaper than “descaling agents” that have the same function.

Iron can be found in water in large amounts. It is a useful mineral, but it gives the water a yellowish-brown color that makes the water less attractive. In addition, much iron can upset sensitive stomachs. In general, we get enough iron through our food, particularly in meat. Spinach has gained an undeserved reputation as an iron source, spinach contains no more iron than other vegetables, that is, very little. Mineral water (and tap water) thus does not noticeably contribute to our need for iron. One of the permitted modifications of mineral water is to remove the iron to take away the brown color.


Besides iron, calcium and magnesium, many other substances are present in small amounts in the water, both in tap water and in mineral water. Many provide important supplements and may be of great importance, including some poisonous in large quantities. Some of them we only get from the water we drink. However, there are some that are always poisonous and have no known function in the body and therefore must be avoided in all water we drink: mercury, lead, arsenic, cadmium and radon.

Mercury is a unique and beautiful metal, but its chemical compounds are very toxic. They are stored in the body and damage the intestines and kidneys. It used to be used in dental amalgam, thermometers and for technical purposes. Now it has been banned except in low energy lamps. The mercury ore cinnabar is unusual and the risk of it coming to the water is low, but mercury was released in large quantities during paper production. The last plants to produce chlorine and lye for paper processing where mercury is included in the process is now closing down after a long political struggle.

Lead has been used for many technical purposes, including to make water pipes, for roofing, and for paints. Lead causes severe damage to the nervous system, kidneys, cardiovascular system and damage to reproduction. It is a byproduct in the production of silver.

Lead poisoning may be caused by lead in the environment. Much of this lead came from additives in gasoline now forbidden. We also spread a lot of lead in the environment in connection with hunting: the amount of lead, most with addition of arsenic, from lead hail and bullets, is so great that it is worrying from a health point of view. The bullets and hail cannot be collected in the fields and slowly corrode. It will stay in the ground for long periods of time and slowly pass to the groundwater.

Lead was used earlier for the manufacture of water pipes, far into the 20th century. The leakage of lead from water pipes is limited if the water in the pipes is cold. Therefore, this was not resolved until the late 1900s in many places, and there are still poor areas in the US that still have old lead pipes left in the water system. This may be a reason why children from these areas are intellectually inferior to their peers from richer areas.

Another cause of lead poisoning is paint color: lead white was used for painting houses until the late 1900s and children who played in houses where the painting flagged chewed on everything, including paint flakes and became poisoned.

Another way to get poisoned: An English couple made a vacation trip to a low-wage country. On the market they bought coffee cups with very beautiful decoration. They used them for their breakfast coffee every day. Eventually, they developed nerve damage. A complicated investigation demonstrated that the decor of the coffee cups contained lead that was released in so large amounts that the English couple was injured for life. Others with nerve damage may not have realized that their beautifully painted porcelain is the cause.

Arsenic is a famous poison, for example, in stories by Agatha Christie. Fortunately, most arsenic poisoning is unintended, mostly from arsenic in drinking water or food.

Famous is the arsenic poisoning through wallpaper around 1900: arsenic was included in green inks for wallpaper. The color was somewhat volatile, so the people who lived in the rooms were poisoned.

Earlier, impregnated wood contained large amounts of arsenic, which ended up in the environment by leakage from the impregnated wood and when the wood structures were demolished and burnt.

Chronic arsenic poisoning manifests itself in skin changes, heart disease and cancer.

Arsenic in ground water is in many parts of the world (luckily not here) a major problem, the arsenic is naturally in the ground and dissolves in the water.

Cadmium: Fortunately, cadmium is taken up badly by the body except in people with iron deficiency. It causes kidney failure. Most of the cadmium comes from dyes, especially in plastic (old plastic articles with yellow or red color are suspicious). To the water, cadmium comes mainly through uncontrolled mining and by rechargeable batteries in the trash reaching the air through uncontrolled burning, then to the water through rain.

Radon: At the beginning of the 20th century, some mineral water producers used the sales argument that the water “contained natural radioactivity”. When everyone became aware of the dangers of radioactivity, the argument disappeared and hopefully also the radon (it can be easily removed from water by bubbling air through it).

Useful in small amounts, dangerous in large quantities

Some substances we get in the water are useful, or even vital, in small amounts but can be very dangerous in larger. This applies, for example, to copper, zinc, selenium, cobalt. Fluorine in small amounts gives strong teeth, but in larger it gives discolored teeth (dental fluorosis). Mineral waters with hydrogen sulphide have a small number of followers, who believe that the stench makes them healthier (it stinks of rotten eggs). Hydrogen sulphide is about as toxic as hydrogen cyanide, but no one is secretly poisoned with it, the stench is far too strong. It has never been delivered in bottled mineral water. Iodine is necessary (otherwise we get goiter) but we get it through iodinated salt.

Neither useful nor harmful

Sulphate in large quantities can speed up the stomach, is not often found in large amounts in drinking water. Silicate (silicon) is found in all ground waters, but most silicates are sparsely soluble so what we get in the water is negligible and harmless. Aluminum is very toxic to the body, but it is not absorbed by normal stomach or intestines, so you only must consider it in water for dialysis treatment.

From the container

Mineral water, with or without carbonic acid, is usually bought in a bottle, in plastic or glass. Both types contribute to the contents of the bottle. In plastic bottles the plastic is released to the water in negligible amounts (1).

Antimony is toxic but no serious health hazard in a modern society, as the four listed in section Toxic. According to some sources, the name derives from the fact that monks in the Middle Ages who used antimony in their alchemy experiments died (anti monk). Antimony is used as an alloy metal in metallurgy, in glass industries and as a catalyst (in very small quantities) in the manufacture of polyethylene terephthalate (PET in pet bottles, terylene and dacron in textiles.) Studies have therefore been made of the amount of antimony released from PET bottles. In the case of drinking water, the highest level is in the percent range the maximum permitted by WHO (3). The amount released to fruit juices is much higher than that given in WHO Recommendation for drinking water, but this recommendation does not apply to fruit juices (4).

Leaks from common white, green or brown glass bottles are silicates of sodium, calcium and iron in negligible quantities. Glass bottles with red, violet, blue or other motley colors can surely leak unknown how much, but we do not often drink such mineral water, so this is probably negligible. Lead leaks from glass and bottles of flint glass, a material used for artistic glass blowing and grinding, but the glass is so short time in contact with the drink that this should not worry us (flint glass contains about 40% lead oxide).


Some of the important minerals we get largely through the water we drink. In some cases, the limits of how much we need and how much are harmful are so close that we should really check how much we get through the water. Some people eat supplemental mineral tablets, but risk getting too much and thus causing serious side effects (for example, selenium in too high dose is very dangerous). Declarations of the content of mineral water are always very short and incomplete, and rarely up to date (the composition changes over time). The same applies to tap water, where I have not seen any information from the water work om the content. We can easily figure out how much we should have, from the WHO’s Drinking Water Guidelines (5) or the FDA and EPA rules for water quality (6) but figuring out how much we really get is more difficult. However, we can safely assume that tablets with mineral supplements without control are more likely a risk than a help.

  • Food and Drug Administration: Guidance for Industry: Bottled Water Quality Standard: Establishing an Allowable Level for di(2-ethylhexyl)phthalate. Small Entity Compliance Guide.
  • World Health Organization: Antimony in Drinking-water, 2003.
  • Shotyk, William et al.: Contamination of Canadian and European bottled waters with antimony from PET containers.
    Journal of Environmental Monitoring. 8 (2): 288–92 (2006).
  • Hansen, Claus et al.: Elevated antimony concentrations in commercial juices. Journal of Environmental Monitoring. 12 (4): 822–4. (2010).
  • World Health Organization: Guidelines for Drinking-water Quality. Fourth edition, 2011.
  • Environment Protection Agency: Bottled Water Basics, 2006, with further references.

These references (except 3 and 4) are available on the internet.