Structure of Water: Water is made up of two hydrogen atoms bonded covalently to one Hydrogen atom. Because a covalent bond is a pair of electrons being shared between atoms, and oxygen has 8 protons compared to hydrogen’s 1, the electrons are greater attracted to the oxygen atom. This means that oxygen is delta negative and the hydrogens are delta positive.
Solid state: When water freezes, it is less dense than liquid water. Pure water only begins to become less dense below 4°C. This is because when freezing the water molecules have less energy so move slower making it easier for hydrogen bonds to form. This leads to an open, crystalline, hexagonal arrangement. This means that its volume increases by around 9%. This lower density means that ice floats so when water in nature freezes the ice floats at the top. If it froze from the bottom up then all the animals would die, instead they survive, and the water is insulated by the ice.
The Universal solvent: Water acts as a universal solvent meaning a lot of solutes will dissolve into it (ionic and polar molecules). Due to water being a polar molecule (one-part delta negative, the other delta positive) this means that the negative ion or slightly negative part of the compound will be attracted to the hydrogen atoms and the opposite applies with the positive. This means that the compound will dissociate. This strong solubility is required for the transport of substances in many organisms such as blood in most animal phyla (excluding Rhombozoa, Kinorhynca, Cnidaria and multiple others). All organisms have cytoplasm as well which requires water to be highly soluble as this allow for reactions to occur.
High Heat Capacity: Water has a heat capacity of 4200 joules, meaning it requires that amount of energy to heat 1 kg of water by 1°C. This allows it to act as a thermoregulator. The reason why water has the highest heat capacity of any liquid is because of the presence of hydrogen bonds. Hydrogen bonds are caused by the delta negative aspects of one water molecule being attracted to the delta positive aspects of another molecule. These intermolecular bonds are weak and easily broken but the presence of multiple is what leads to this unusually high heat capacity. This means that water acts as a great habitat as it isn’t susceptible to wild temperature fluctuations, meaning organisms won’t experience them. It also allows for highly regulated internal body temperatures and is why our temperature never drastically drops or rises to the ambient temperature.
High Boiling point: For the same reason as the high heat capacity, water has a very high boiling point and is an anomaly on the trend due to its low molecular weight. Hydrogen sulphide has a boiling point of -62°C, this is the hydride before water yet it’s boiling point is over 150°C lower. This is because more energy is needed to break all of the multiple weak hydrogen bonds which hold the molecules of water together. This is also the case for it’s freezing point. This feature is incredibly important as if water continued the trend it would be unlikely for liquid water to exist where it does on our planet as it would instantly boil somewhere near -100°C. As water is the assumed starting point for all life it would be unlikely that any organisms would be here today as there would never have been a suitable habitat to begin with.
High Surface Tension: Apart from mercury water has the highest surface tension of any liquid. At the surface of water there are water molecules to be found below and at the sides of other water molecules but not above. This means that there is a strong pull down and out but not up due to a lack of hydrogen bonds from above. This allows for water molecules to be more densely packed at the surface meaning that the hydrogen bonds are stronger creating surface tension. This allows water droplets to exist and keep its shape as the molecules are more attracted to each other than the surrounding air due to the hydrogen bonds. This metaphorical “film” allows for certain insects and objects of greater density to stay above the water instead of sink such as water boatmen or the Basilisk lizard (a much larger organism than an insect which utilises the surface tension and its speed to escape prey creating its common name the “Jesus Lizard”). If water had a much lower surface tension even the smallest of particles would fall to the bottom leading to the collapse of ecosystems as surface-feeders would not find any food, such as many species of fish and aquatic birds. It also allows for water to be transported up the xylem tissue, an essential process for vascular plants, as it allows for capillary action.