The taste of water
Water (H2O) has no taste.
There are receptors for sweet, sour, salt, bitter and umami (savoury). There is no water receptor.
If water has a taste it is due to the substances dissolved in it. Water from the tap has many things in it.
Hard water has a high mineral content in contrast to soft water, the minerals in hard water are calcium and magnesium. The hardness of water depends on where you live as well as what is done to the water before you drink it. As rainwater falls it is naturally soft (nothing in it). With time carbon dioxide from the air dissolves in the rainwater and this forms carbonic acid - a weak acid but strong enough to dissolve some calcium and magnesium from regions containing chalk increasing its mineral content and rendering it hard. There is a scale of hardness (in mg of CaCO3/L or ppm); soft <60, hard = 120-180, very hard > 181. In the UK, Manchester's water is 25, London's is 275; in the USA >85% of homes have hard water (120-180); in Australia Melbourne's water is 10-26, Sydney's is 39-60 and Adelaide has hard water, 130-148 (all units ppm). Hardness may be inconvenient, it causes deposits on pipes, heating systems and prevents soap from lathering but calcium and magnesium are required for normal metabolism and the lack of these ions in soft water has possible health impacts including risk of heart conditions. 1000mg per day of calcium is recommended for adults. Many bottled waters have these minerals removed (more later).
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| David Hockney |
Rainwater maybe soft but does not have a neutral pH. Pure water has a pH of 7.0 but rainwater is 5.6 (acidic) because it picks up carbon dioxide in the atmosphere as it falls and this forms carbonic acid as we saw already. The pH of tap water ranges from 6.5-8.5. Water is safe to drink in this range and bottled waters range from pH 5.5 (Perrier) to 9.5 (Essentia). You can test the pH of your water using paper indicator strips. Water with a low pH can leach metal ions such as iron, manganese, copper, lead, zinc (from pipes for example) giving it a metallic or sour taste. The primary way to treat acid water is to neutralise it with soda ash (sodium carbonate and sodium hydroxide) and this increases the sodium content of the water. A pH greater than 8.5 indicates that the water is hard and causes an alkali bitter taste and will cause scale deposits on dishes, laundry and difficulty on getting soaps to foam.
The pH of common liquids: vinegar 3.0, wine 2.8-3.8, beer 4.0-5.0, milk 6.3-6.6, seawater 8.3 (neutral = 7.0)
Water can contain numerous other contaminants including bacteria, giardia (a single celled parasite), volatile organic compounds like trihalomethanes produced during the control of micro-organisms with chlorine and very often it is not safe to drink.
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| Giardia parasite |
In countries where the water is safe to drink great trouble is taken to make it so. Public bodies take pride in the provision of clean, healthy water for their population. The Washington Suburban Sanitary Commission (WSSC), Maryland, USA for example publishes a careful analysis of its water annually. To be safe many authorities add chlorine to their water. Anglia Water (UK) admit to adding chlorine (1mg/L; it's 1.5-5mg/L in public swimming pools) to the water supply and give advice about what to do if your water tastes a bit funny. Sydney (AUS) water is monitored and the results published quarterly in astonishing detail, you really know what you are drinking in Sydney - chlorine is added at around 1mg/L.
In many countries you have to drink bottled water but in countries where the tap water is quite safe to drink fashion dictates that people drink bottled water. 20,000 bottles of water are bought per second globally, 480 billion bottles of water were sold in 2016. A study in 2011 of 170 bottled waters in the USA found that 40% were tap water either treated or untreated. The majority of bottled water companies use extreme filtration (eg ion-exchange, demineralisation, reverse osmosis, distillation, deionization) resulting in "dead" water, void of all healthy minerals. The bottles are largely made from polyethylene terephthalate (PET) which is recyclable but less than half the bottles were collected for recycling and only 7% of them were made into new bottles. The rest ended up in landfill or the ocean. There is currently a petition to the United Nations to recognise a plastic island (the size of France) in the Pacific Ocean as an independent country. The explosion of plastic bottled water has become a political issue. It undermines the ongoing commitment to safe collective water provision in the interest of the common good.
Another reason to worry about bottled water is that almost all plastics contain chemicals with oestrogen activity that leaches into the water. These chemicals can produce many health-related problems, such as early puberty in females, reduced sperm counts, altered functions of reproductive organs, obesity, altered sex-specific behaviours, and increased rates of some breast, ovarian, testicular, and prostate cancers.
Filtering your own tap water with activated carbon may provide a solution. Active charcoal carbon filters are most effective at removing chlorine, sediment, volatile organic compounds (VOCs), taste and odour from water. Filters containing activated carbon (e.g. Electrolux filtro de agua, Brita filters) are quite good at removing oestrogen as long as the filter is fresh. However, activated carbon does not filter dissolved solids including minerals, salts or metals such as iron that are not considered contaminants; neither does it filter inorganic contaminates such as lead, arsenic and asbestos or most microbiological contaminants (eg bacteria). Radionuclides are not filtered although these may be reduced. If you are worried about micro-organisms then purification of water contaminated with viruses, cysts and bacteria can be achieved with chlorine dioxide tablets without leaving an aftertaste.
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