There is no such thing as naturally pure water; all waters we drink contain dissolved solutes and many contain some microorganisms . Indeed, drinking 'pure' water even if obtainable, when it would be very expensive and prone to unwanted materials being introduced during its production and storage, is not a healthy option as important minerals are absent . There are several forms that the water we drink may take, which vary subtly from each other; drinking water, spring water, tap water, natural mineral water and water preparations promoted with various health claims. Bottled waters are subject to international regulations but are not necessarily safer than tap water. Clearly, all such water must be drinkable, contain solutes (including those classed as contaminants) below the legally-allowed limits, to be bacteriologically safe and be subject to continued monitoring.
Tap water Water, from any source, treated to meet legal and quality standards. It may contain low or moderate amounts of minerals depending on the source of the water (for example, hard or soft water areas). This is the major water product with over a billion glasses a day being consumed in the US alone, although most domestic tap water is used for washing, flushing the toilet and through wastage. Often it is chlorinated, which ensures microbiological safety for long periods of storage and eliminates all risks from otherwise devastating diseases such as cholera and dysentery. Although chlorination has been shown to possibly produce potentially hazardous byproducts, the association between exposure and demonstrable adverse health effects is still unproven and the protection chlorination offers far outweighs this risk. Fluoridation of water (for example, by adding SiF62-) for the purpose of reducing dental caries, is generally regarded as safe [966a]. However, groundwaters containing excessive amounts of fluoride (> 1 mg/liter) are widespread [966b]. The health claims for fluoridation remain controversial .
Drinking water Water intended for human consumption and may contain disinfectants and/or other solutes within legal quality standards. Such bottled water is not necessarily better for health than tap water, as shown in 2004 when Coca Cola was awarded an Ig® Nobel prize for producing Dasani in the UK. Dasani was a bottled 'pure' water prepared from London tap water. It was found that it contained high levels of the carcinogen bromate, which is (and was) not present in the tap water. The bromate was introduced by reaction between the added ozone and calcium chloride containing calcium bromide during production (for background Science see ).
Natural mineral water Water from a spring, artesian well or well that naturally contains dissolved salts . It may be carbonated. It is characterized by its mineral content, which may vary between far lower to much higher than tap water, according to source. Mineral waters must be naturally safe with no parasitic or pathogenic organisms as they are not subject to disinfection. The presence of safe microorganisms is used as proof that no disinfection has taken place. Higher silica content distinguishes mineral water from surface (for example, reservoir) water. The price of mineral water is over a thousand times that of quality tap water.
Spring water Water from an underground aquifer, collected as it flows and bottled at source.
Processed water with health claims There is an increasing market in bottled water and domestic water processing equipment claiming that the water has considerable health benefits varying from more rapid hydration to cures for AIDS and cancer. Generally there are no proper scientific trials to prove these claims, only isolated testimonial evidence. Oxygenated drinks have been proposed to improve the immune status. However, a randomized blinded clinical study , although showing a transient moderate increase in oxygen radicals (using 6 mM O2) and signs of activation of the immune response, was not conclusive.
One factor often used to promote these ‘health’ waters is supposed greater cellular hydration or ease of hydration. It is unclear whether increased cell hydration is actually health-promoting. A recent paper has argued that this may be a determining factor in the initiation of cancer . It has been found that cancer cells do have greater water with increased fluidity but the cause and effect relationship (that is, whether increased cellular hydration initiates cancer or cancer initiates high cellular hydration) has not yet been established.
‘Sports’ drinks Sports drinks  are intended to reduce fluid, mineral (e.g. particularly Na+) and energy imbalance due to exercise. The carbohydrate content and osmolality must both be low to encourage efficient hydration (that is, the drink must be hypotonic (<280 mOsmol/L) or isotonic (~280 mOsmol/L)). Na+ ions (usually as NaCl) are a necessary ingredient as they stimulate both Sugar and water uptake in the small intestine as well as replacing material lost by sweat. Hypotonic drinks give more rapid hydration but clearly contain less Sugar and minerals. Chilling improves palatability so encouraging consumption. Some sports drinks contain ‘power’ ingredients such as caffeine or taurine, where there is patchy evidence of some sports benefit. These products are usually promoted with testimonials from athletes or sports teams, but without double-blinded trial evidence.