The amazing properties of water and how to test them

Earth, fire, air, and water have long been considered prime elements and essence of all life. Now we know those “natural forces” are not really elements, but something else entirely. Fire, for example, is a chemical reaction between oxygen in the air and fuel such as wood or coal. Earth and air are actually combinations of many different elements.

Water is a molecule, composed of 2 hydrogen atoms and one oxygen atom. But, ancient philosophers got one thing right - water is essential for life. There is a reason why all ancient civilizations were founded next to the rivers. Life, as we know it, depends on water.

Water in the human body

Our body consists of 65% of water. That’s amazing! But what’s more interesting is that certain organs like the brain and the heart (73%), as well as the lungs (83%), depend on water consumption even more.

All humans and living beings are made from a lot of water

Water is our essential need. You have probably heard that we must drink two litres a day, but that is one of the stickiest myths going. Health guidance actually talks about total water intake of roughly 2.7 litres for women and 3.7 litres for men, and that counts everything: tea, milk, juice, soup, and the water inside food. About a fifth of it we get from food. There is no magic number to hit, and thirst does a solid job of telling us when to drink.

What is true is that even mild dehydration is no fun. It is linked with headaches, tiredness and trouble concentrating, which is a good enough reason to keep a bottle of water nearby on a hot day. In our body, water has multiple roles. Maybe the most obvious is that it regulates our temperature by sweating. But even more importantly, it provides fuel for every cell in our body. It’s also used to metabolize and transport food as well as to flush waste. It forms saliva needed for digestion and lubricates joints. Water is really essential for our everyday functioning.

Chemical structure of water

Structurally, the molecule of water looks like a letter V. The formula for the water (H2O) is probably well known to everyone. Two hydrogen atoms bond with one oxygen atom by what is called a covalent bond. That means that electrons are shared between the oxygen and hydrogen atoms, not transferred.

Oxygen is the more electronegative of the two, more “greedy” for electrons, so that part of the molecule has a slightly negative charge. The other part (the hydrogen part) has a slightly positive charge. This type of molecule, with differently charged ends, is called a polar molecule. That polarity makes water molecules highly attracted to each other. The positively charged end of one molecule is attracted to the negatively charged end of another water molecule. We say that multiple water molecules are connected by hydrogen bonds. That allows for some interesting properties we will discuss next.

Adhesion and cohesion

Cohesion and adhesion define “stickiness” of a substance. Cohesion is an attraction between similar things, while adhesion is an attraction between different things. Water has high cohesion, it is actually highest of all nonmetallic liquids. That means that molecules of water like to stay close together (remember hydrogen bonds?). You can see this property in action if you observe a drop of water on the wax paper. A drop of water consists of many water molecules bonded by a hydrogen bond and it retains its shape.

Adhesion and cohesion at work. See how water behaves differently

But there are cases when the attraction to other types of molecules overpowers cohesion.

Did you ever observe water on the glass? It becomes a wet mess, unlike elegant drops we saw before. Why? Well, glass molecules are even more polar than the water, so they become more attractive. This is adhesion. Adhesion and cohesion work together to achieve some really amazing things. One of them is capillary action, movement of water upwards, against the gravity. This is the principle on which the plants transport water around and it also helps with blood circulation in our body.

The universal solvent

A solvent is a thing which can dissolve other things. And water can dissolve more things than any other liquid. That’s why it’s often called the "universal solvent". Those things which we put in liquids are called solutes.

Since water is polar, it can dissolve other polar molecules and ionic compounds. Examples include table salt, food colors, and sugar. Since they dissolve in the water we call them hydrophilic molecules. Those that do not mix with water, such as oils, we call hydrophobic, water-fearing molecules. They do not dissolve in water since they are nonpolar. Nonpolar molecules interfere with the hydrogen bonding of water molecules. We explored more this topic in our Lava lamp experiment so try it out if you’re interested.

Density and heat capacity

Did you know that water is the only substance we find naturally in all 3 forms on Earth: solid, liquid and gas? Plenty of substances can exist as a solid, a liquid and a gas if you push them hard enough - iron will do all three, given a hot enough furnace. What makes water remarkable is that it does all three at the ordinary, everyday temperatures found at the Earth's surface. Snow, the sea and the clouds above it are all the same substance.

And another peculiarity: the density of water is higher in liquid form than in solid (ice). But how is that happening? Around 0 degrees Celsius, hydrogen bonds start forming crystalline structures. In crystalline structures, atoms are more spread apart so the density is lower. That’s why the ice floats on the water!

Here is the part most people never hear: water is at its densest not at freezing point but at 4 °C. So as a lake cools in autumn, the coldest water sinks only until it hits 4 °C, and after that the colder water stays on top and freezes there. The lake ends up with a lid of ice and liquid water underneath - which is exactly why fish can spend the winter down at the bottom.

The density of the water is higher in a liquid form than in solid

Water has a very high heat capacity - the highest of any common liquid. (A few substances beat it, liquid ammonia among them, but you will not meet those in a kitchen.) That means it can absorb a lot of heat before its temperature rises. The opposite is also true: water cools down slowly. If you’ve ever been around the sea, you know the climate is much more pleasant. Water serves as a buffer that prevents huge differences in temperature.

Since the human body consists of much water, this property also helps us in regulating body temperature. Think of the various temperature conditions we find ourselves in, from freezing winters to scorching summers. We can manage it without many issues because our body uses water as a temperature buffer. If you want to see water’s heat capacity in action, check out 5 amazing balloon experiments where we explored it in details.

Test the properties of water yourself

Reading about water is one thing; catching it in the act is better. Here are three quick tests, each one showing off a property we just talked about. Everything you need is already in the kitchen.

1. How many drops fit on a coin? (cohesion)

This one shows cohesion - how strongly water molecules cling to each other.

You need: a coin, a cup of water, and a dropper (a straw with your finger over the top works too).

Put the coin on a flat, dry surface and add water one drop at a time, counting as you go. Long after you would expect it to overflow, the water keeps piling up into a wobbling, see-through dome on top of the coin. It is the hydrogen bonds pulling the surface molecules together into a "skin" that holds the dome in place, until finally one drop too many breaks it.

2. The colour-climbing celery (capillary action)

This shows capillary action, the cohesion-and-adhesion team-up that lets water climb upward against gravity - the very thing plants use to drink.

You need: a stick of celery with its leaves (a pale flower like a white carnation works beautifully too), a glass of water, and some food colouring.

Stir plenty of food colouring into the water, trim the bottom of the celery, and stand it in the glass. Leave it for a few hours, or overnight for the full effect. The colour creeps up the hidden tubes inside the stalk and reaches the leaves, staining them. Slice the celery across afterwards to find the coloured tubes it travelled through.

3. The fleeing pepper (surface tension)

This shows surface tension, the skin that cohesion creates on top of the water - and how soap breaks it.

You need: a shallow bowl or plate of water, ground pepper, and a drop of dish soap.

Scatter pepper across the water so it floats on the surface skin. Now touch the middle of the water with a finger dipped in dish soap. The pepper darts to the edges in an instant. The soap breaks the surface tension where you touched, and the taut skin left around the edges pulls back and drags the pepper with it. It is the same soap-versus-water trick behind our colourful milk experiment.

Frequently Asked Questions

And that is all from us but just the beginning for amazing water. If you enjoyed this article, we recommend that you experiment a little. Why don’t you try to make your own plastic? Or go explore osmosis with gummy bears or Diffusion with hot and cold water. Many, many exciting scientific adventures await you.