Water - the basis for life

The water on earth is virtually as old as the planet itself being approximately 4.0-4.5 bilion years old. Most of it may be older than the oldest rocks ever found on earth. There are a number of theories as to how it got here. Some involve water containing rocks hitting the earth about 4 billion years ago. Others consider that water was released from the rocks inside the earth as it cooled down. The majority of water molecules on earth have remained intact since those ancient times. 

Safe drinking water is available to nearly 6 billion of the world's 7 billion inhabitants, although only about 55% of people have tap water piped into their homes(1). We drink this water either directly or indirectly via cooking, washing fruit and vegetables, and in diluted hot and cold drinks. 

Types of water

Tap water

The water you get from your tap can vary depending on where in the world you live, how your water is treated and what pipes you have leading into your house. You can adjust the water quality by using a water filter.

Hard water

Hard water is normally defined as water containing more than a specific amount of certain minerals in it. The minerals responsible are those that form charged particles called ions in solution. Minerals that form ions with 2 or more charges (missing electrons) are the ones responsible. They are normally calcium and magnesium, although iron, aluminium and manganese can also contribute to hardness. Minerals that form ions with only one charge such as sodium (think salt) and potassium are more likely to soften water.

Hard water creates rings around your bath, furs up your kettles, requires more soap for washing and more detergent for laundry. It is also associated with better long term health. In particular magnesium salts are often associated with reduced risk of fatal heart attack and strokes. Calcium salts have been associated with reduced risk of a number of cancers, including relatively serious ones such as gastric cancer. Some people are deficient in calcium and magnesium and this could be partly the reason for these associations(2).

The measurement of hardness is based on an equivalent amount of chalk (CaCO3) dissolved in the water(3).

Soft water

Soft water is good for producing lathers from your soap and is better at cleaning your hair and making it feel soft. Some people report that it can leave your hair flat and lifeless, although this depends how curly your hair is in the first place. For those with curly, hobbit like hair it probably improves appearance!

In terms of health it appears to be associated with more heart disease and cancers, although we should remember that not all studies have found the link between hard water and increased health. However, the weight of evidence does seem to point to a protective effect for people in hard water areas.

Bottled waters

Bottled water is more often sourced from ground water than tap water. Because ground water tends to be harder than surface water it follows that bottled water from groundwater sources is generally harder than much tapwater. In the UK, bottled waters are divided into 3 categories: mineral water, spring water and drinking water(4).

Mineral water

Water from a underground source recognised by the Government. Any water treatments must also be restricted to filtration or carbonation.

Spring water

Spring water, well water and artesian water all come from underground aquifers that must be shown to be "unpolluted". Well and artesian waters are retrieved via a well. Spring water flows to the surface naturally before being bottled. Water treatments can be applied to kill microbes and comply with drinking water standards. Unlike mineral waters, spring waters are not so tightly defined.

Drinking water

This could be pure tap water, or it could be tap water that has undergone filtration or distillation. It may come from more than one source and is often treated so that it complies with drinking water regulations. Mineral salts may be added for marketing purposes.

Tap, bottled or filtered?

Tap water

Tap water often originates from streams and rivers. It is often treated with chlorine or chloramine, which help disinfect the water as it travels through the pipes to your home. It can however leave a distinctive taste. It can also be treated with ozone and UV rays to kill more microbes. The water supply in some areas may also contain flouride, which is associated with low thyroid function and a slightly increased risk of bone cancer(5).

If you live in a house built before the 1970's in the UK then you may well have lead pipework which could increase your toxic load of lead.

Bottled water

Bottled water generally comes from ground water, which has a more consistant taste and composition than tap water. The taste is further protected as the water is normally treated with ozone to minimise the residual taste. However plastics in the bottles themselves may leach into the water affecting the taste, especially in hot weather.

Bisphenol A (BPA) and other components of plastic bottles can leach into the water. There are links between BPA exposure and reductions in insulin sensitivty and formation of new fat cells, two effects that could lead to weight gain(6). So your healthy drinking habit could actually be leading you to gain rather than lose weight!

Filtered water

Water filters are generally designed to remove contaminants that may be found in tap water. These include: arsenic, lead, nitrate, nitrite, chloroform, chlorine, fluorine, radon and E Coli. However, different filters vary a lot, and if you buy one it makes sense to know what is wrong with your water first otherwise you could be wasting your money. Filters may remove:

  1. Carbonates from water, making it less hard.
  2. Chlorine via the presence of activated carbon.
  3. Microbes that have survived the chlorination of tap water supplies.

In theory filtered water may be less healthy than tap water if it is softer. On the other hand some unhealthy impurities may be removed by the process.

How much should I drink?

How much water you need to drink depends on a number of factors: Your body size and make up; how much exercise you do; how many fruits and vegetables you eat, your state of health as well as the temperature and altitude where you live.

There is a widespread urban myth that you need 8 glasses of water a day. Of course this is only going to be true for a few people. Some will fare better with more, and some with less. 

For most people drinking when you are thirsty is perfectly adequate to maintain hydration. In general thirst kicks in when your blood concentraton rises by about 2%, while dehydration is defined as beginning when your blood concentration is increased by at least 5%(7). So in theory then you have a buffer of about 3% between getting thirsty and putting yourself into a dehydrated state.

For some people, such as those with diabetes, kidney disease, the elderly, or those doing strenuous exercise, the thirst mechanism may not work properly. In these cases, a drinking routine should be initiated to avoid dehydration.

A rule of thumb for determining if you are drinking enough fluid is to check how many times you go to the loo each day. It should be roughly 4-5 times, and the colour of your pee should be straw yellow. 

Sports Performance

A lot of people don't realise that most elite endurance athletes will complete races such as the marathon, with a blood concentration of between 5-8% above normal. This makes a mockery of the widespread advice that sports performance levels reduce markedly when blood concentration increases by as little as 2%. 

DrDobbin says:

Tap, bottle or filter?

I'm not a great fan of bottled drinking water. Certainly if your tap water is hard, tasty and free of serious contaminants then it is a huge waste of money to buy bottled water. However, there are times when it may be prudent to use bottled water, such as when travelling abroad and you may be exposed to bugs that can provoke your immune system.

Water filtration should only be neccssary if your water is contaminated. Some people worry about the levels of various contaminants and if you are worried too then take a look at your local water authority report. This is easy to do the the US and UK. A long list of microbes, metals and organic contaminants is normally available showing legal limits for each. Average, minimum and maximum levels in your local area for each of these are normally available.

Unfortunately some contaminants don't have legal limits set or have limits that many consider are set too high. Chlorine, fluorine, trihalomethanes and cryptosporidium are often considered in these categories.

I looked at mine and discovered that only slug bait - metaldehyde was showing over legal limits. I looked it up and concluded that at 4 times the legal limit it was unlikely to be causing harm(8).


1) http://www.who.int/water_sanitation_health/publications/2013/jmp_fast_facts/en/index.html

2) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3775162/#!po=3.84615

3)  To be considered hard, water must contain >120mg/L of chalk.

4) https://www.gov.uk/food-standards-labelling-durability-and-composition#bottled-water

5) http://www.drdobbin.co.uk/fluoride-it-safe-fluoridated-water

6) http://www.jlr.org/content/43/5/676.full

7) http://www.ncbi.nlm.nih.gov/pubmed/12376390

8) http://waterquality.anglianwater.com/mergedreport.aspx