WHAT WATER CONTAINS

Good and bad things

Absolutely pure water contains only the molecule H₂O. It does not exist in nature, and the absence of minerals makes it unsuitable for drinking.

Natural water contains dissolved substances, mainly inorganic salts (minerals) originating from the geological layers through which the water has passed. To be healthy, water must contain some of these minerals. The human body is quite flexible and accepts a wide variety of water compositions (see the first table on my main drinking water page). Body cells, and the blood, contain electrolytes (salts). Water without any salts—distilled or demineralised water—is bad because of an "osmotic effect": the salts in the cells or blood may migrate into the water and deplete the normal salt concentration in the body.

Inorganic salts
These are made of cations (positively charged) and anions (negatively charged) dissolved in water. The most common of these ions are:

• Calcium Ca²⁺
• Magnesium Mg²⁺
• Sodium Na⁺
• Potassium K⁺
• Bicarbonate HCO₃^– (called officially hydrogen carbonate)
• Sulphate SO₄^2–
• Chloride Cl^–
• Nitrate NO₃^–
• Fluoride F^–

The above ions are beneficial or neutral. Their concentration may vary between a few mg/L (or ppm) and a few hundred mg/L. The last two, principally fluoride, should not be present in high concentration. Nitrate is relatively harmless for adults, but can cause severe diseases with infants. Other details in my main water page.

Other minerals and oligo-elements
Natural water may contain many other elements in lower concentration, notably metals such as iron, zinc, copper etc. Some are considered good (a little iron, copper or zinc) whereas other metals are toxic, such as lead, cadmium or uranium which are "heavy metals". The word "oligo-element" is used without a precise scientific definition and indicates that some metals are considered favourable for health.
Other dissolved elements that are not metals are toxic at various concentrations: arsenic, selenium or boron for example.

Other natural substances
Water contains other dissolved natural substances:

• Oxygen O₂
• Carbon dioxide CO₂ (the bubbles in sparkling water)
• Silica SiO₂
• Organic matter resulting from the decomposition of vegetals (leaves, grass) in surface water (rivers, lakes and ponds)
• Bacteria, also in surface waters

Borehole (deep well) waters contain usually very little organics or bacteria: they have been naturally filtered by the soil. In many cases, they are suitable for drinking without any treatment.

Man-made contaminants
These are unfortunately many. Some of them only increase the concentration of ordinary minerals such as sodium, chloride, sulphate or nitrate. Some produced by agriculture or industry are clearly undesirable or toxic:

• Pesticides and insecticides, of which many have a very long lifetime and are not bio-degradable and may create health problems
• Pharmaceutical residuals
• A wide variety of heavy metals (Pb, Cd, U, Ni, V, Mo, W, Mo, Co, Cr etc.)
• Arsenic (As), fluorine (F), boron (B), antimony (Sb)
• Various hydrocarbons mainly from petrol, domestic fuel and engine oil leakages or from the petrochemical industry
• Phosphate PO₄^3– which is not toxic but creates undesirable effects on the environment (eutrophisation of the rivers)
• Leakages from old garbage dumping sites

The World's Health Organisation (WHO) and various European or national authorities give recommendations and publish laws limiting the concentration of all these contaminants in drinking water supplies. Although these specifications are not uniform or identical, some apply to tap water and some to bottled water.

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