Water – Chemistry 101

Dihydrogen oxide kills hundreds, if not thousands across the globe annually. It is also the most potent Green House Gas (GHG) we have. It is water of course and it sometimes gets a bad rap.  In the last few days I have come across a number of water stories that show how misunderstood our friend water really is.  These have included cars that run on salt water, tap water being full of chemicals, we need to drink alkaline water (or ionised water) and we will all be sucking water directly out of the air using modern technology (MOFs).

Basic Chemistry

Let’s start with the basic chemistry of water. It is a molecule with two hydrogen atoms and one oxygen atom and is produced as a result of burning hydrogen in the presence of oxygen, releasing energy in the process.

2H2 + O2 => 2H2O

Pure water is the end product of this combustion process and it has no energy from combustion left. Water does not burn and has no calorific content.  There is no process known that will get more chemical energy from the water even with added salts.  You could from controlled nuclear fusion of the individual atoms but we are nowhere near that at this point in time.  You can also use the water to store potential energy by pumping it up a hill (and letting it flow back down).  This process requires more energy to pump back up than you get from letting it flow down (due to losses of energy on the way).

You can reverse the process where 2H2O => O2 +2H2 by electrolysis, but this process requires more energy than you originally put in (so there is no net gain in energy).

Water acidity, molecular size and shape

Pure water is not acid, nor alkaline. It has a pH of 7, right in the middle. To be acidic it would need excess  ions or to be alkaline it will need more  ions. An atom that gains an electron is called a negative ion and vice versa.  The pH scale is a logarithmic scale that measures the presence of hydrogen ions ().  While water naturally splits into these ions where H20 =>  + (or more correctly 2H2O => +) the amount of these ions in water is miniscule. In fact it is a constant called Kw  =  at standard temperature and pressure . On a negative log (base 10) scale we then have pKw = 14 (logarithms will come up in the maths blogs shortly).  We also define pH on this scale where pKw = pH + pOH and for pure water this is simply 14 = 7 + 7.

The molecular state is much more stable than the ionic state.  There is no known process to ionise pure water any further.  So pure water can not be ionised and is pH neutral.  Any positive ions present are neutralised by equal numbers of negative ions.  Adding impurities is likely to change the pH (ie acidity)

A water molecule is a well defined shape making an angle of 105 degrees between the three atoms and a bond length around 0.1 nano metres (nm). This makes it one of the smallest molecules that exist and allows us to filter it with a molecular sieve (eg water desalination by reverse osmosis).  This shape also makes each molecule slightly charged, with the hydrogen side being a little more positively charged. Each molecule has an attraction to the next creating a weak stickiness called a hydrogen bond.  This keeps water molecules clumped together somewhat randomly.  They can not be further manipulated into hexagonal rings or other shapes as has been suggested by some dealers of specialised waters.

Universal Solvent

Water is often called the Universal Solvent as many substances are at least partly soluble in water. It is easy to make water slightly acidic by adding an acid.  One way we do this daily is by adding a little acid (citric or ascetic for example).  Another is by dissolving carbon dioxide in it (ie sparkling water).  We can also make it alkaline by adding calcium or bicarbonate (baking soda is an easy product to come by).  Contaminants make water acid or alkaline, not ionisation.  There is no such thing as acidic or alkaline pure water. A lot of contaminants (generally known as salts) disassociate into ions when dissolved in water.  A lot of these ions will react to form other compounds which will precipitate (calcium carbonate, or magnesium sulphate for example).  The most long lived (least reactive) ions are Sodium (Na plus) and Chloride (Cl minus), which is why they dominate sea water.

Underground water, generally called bore water (or sometimes spring water) will naturally contain dissolved solids from the rocks it has passed through. These may be beneficial or harmful and may make the water more acid or alkaline, depending on what dissolved materials are present.  People selling each of these waters will obviously try to show that their particular water has the most beneficial health qualities. While your body needs an assortment of minerals it is unknown (or unproven) whether mineralised water is good or bad for any particular individual.  Too much may damage your kidneys and natural pollutants like arsenic may kill you!

Alkaline water generally has a pH of around 7.5 to 9 while stomach acid is around 1.5 to 3.5. As pH is a logarithmic scale each drop of 1 unit below 7 is a ten fold increase in acidity.  Stomach acid will almost certainly neutralise any alkaline food or drink that enters your system.  From there the food enters your small intestine and is absorbed into the body.  It is at this level that some maintain that what you eat will determine how acid your body is.  Science tells us that the different parts of the body have different levels of acidity (stomach is acid, blood is alkaline) and that the body maintains these levels whatever we eat.  Whether your water is acidic or alkaline probably makes very little difference (it has not been proven either way).

Science also suggests that consuming too much alkaline water may be harmful to your kidneys. There are many theories on what is the most healthy and on what happens to various foods as they are absorbed by our bodies.  These theories come about much quicker than anyone is able to study them thoroughly, so each of us needs to make our own decisions on what might be beneficial or not.  Just remember that any underground water may be contaminated by naturally occurring toxins ( eg arsenic) or bacteria, as well as those toxins put there by human activity.

Which water is best?

So what water should we drink? When I grew up, rain water was always thought of as the best quality drinking water. Evaporation gives pure water which falls as rain and is then collected, which on first consideration seems like great water quality. Rain water will however dissolve pollutants in the air and from your rooftop and is generally stored in plastic tanks with no disinfectants or additives.  Probably not too bad if you live in an area with few air pollutants, little dust and bird droppings and cold climate.  A bit more problematic otherwise.

So is bore water better? Bore water will contain whatever is soluble from the rocks the water has passed through and needs to be checked for toxicity.  It will also contain dissolved hydrocarbons as these are simply organic matter particles that have been cooked up in the earth.  Bore water / spring water will be very different in different parts of the world.  Bore water may also contain pollutants from the bore and any bore cleanup activity.  The good news is that the earth is a pretty good filter.  The other good news is that bore water may contain beneficial minerals.  Bore water is also probably not disinfected.

Bottled water then? This is essentially processed bore water.  It is unlikely to come from a mountain spring as there is just insufficient quantity to provide for all the world’s bottled water.  It is also likely to be tap water.  At least it is tested (hopefully), filtered and disinfected.  Water for drinking purposes needs to be disinfected.  It may then be filtered to remove remnants of the disinfection process (ie a molecular sieve).  Disinfection is mostly done using chlorine (or hypochlorite which releases chlorine).  It may also involve UV light and or passing ozone through it (often called triple disinfection).

Bottled water is stored in plastic bottles of various quality and are banned in various localities. Significant energy is used and GHGs created making plastic bottles as well.

Desalinated water? This has removed anything larger than water molecules by a process called reverse osmosis. It leaves smaller molecules like Boron which are likely to be present in sea water (and some bore water) in the final product.  While very small quantities are necessary for good health larger quantities are considered toxic (thought to be a cause of arthritis).  Desal plants are likely to have a boron removal process attached.  Once everything is removed we have nearly pure water.  Salts (electrolytes) are then added to help with the taste.

Tap water anybody?  Again this is highly variable in quality and ingredients.  If the catchment is well controlled, the water processed effectively and the pipes are in good condition, tap water is probably similar quality to bottled water.  If you leave tap water sit in an open container any remaining chlorine will dissipate.  If you leave it too long it is likely to turn green (caused by a generally harmless algae).

Chlorine will break down to chloride ions in the normal process of disinfection, the same ions as in sea water.  Tap water should have some remaining active chlorine to ensure that the water is bacteria free as it comes out of your tap. The World Health Organisation has stated that the “risks to health are extremely small in comparison with inadequate disinfection”.

In unusual situations (hot weather, abnormal organic pollutant levels – eg a dead animal) excess chlorine will break down into other compounds called HBPs (halogenated by products – halogen is another name for chlorine like atoms).  These include THMs (Tri Halo Methanes like chloroform) and HAAs (Halo Ascetic Acids).  These can be filtered by using a carbon filter on your taps or by leaving water to sit for a time.

In smaller cities we have pretty good quality tap water in general. The city of Flint in the US may beg to differ as their town water was (is?) contaminated with lead due to poor water management!  Large cities may recycle waste water as tap water.  This should be filtered and tested to ensure no unwanted impurities.  It also needs to be disinfected.  Large parts of the world’s population have no options but to drink contaminated water, with diseases like cholera prevalent.

Clear as mud! All water is contaminated.  Marketers can sell some contamination as “good for your health!”  Levels of chlorine breakdown by products are likely to be substantially lower than that required to cause you a health problem.  If you are really worried about them then don’t go near a swimming pool!

… and that method of water from the atmosphere using a MOF (Metal Organic Framework). Might be great for emergency situations and for those living in deserts, but our rainwater system already collects water from the atmosphere at very little cost!

… and the answer to all the questions is NO!