Living things need water for many reasons. One of the most important reasons is that water can dissolve many substances that organisms need to survive, and carry these substances to their destinations.

The way that life has developed on Earth, other liquids such as oils and alcohols would be inappropriate for dissolving and carrying these substances because oils and alcohols may also dissolve and disrupt cells. Another crucial reason is that water helps regulate the acidity (measured by pH) of the mixtures in all organisms. Many living organisms prefer to stay at neutral pH, which means neither acidic or basic, and water helps with this stabilization process. Changing the acidity of solutions in living organisms changes the chemical reactions that can happen in these organisms and therefore the entire process of life!

A third, equally important reason is that water helps maintain the right pressures of cells in living things, by coming in and out of cells constantly. Imagine a balloon that pops from too much air pressure on the inside, or a balloon that collapses from too much air pressure on the outside. Without water, our cells would pop or collapse from too much pressure on the inside or outside like the balloon. These are just a few of the reasons that living things like us need water.

Life uses water as a solvent: all of the chemical reactions that sustain life happen in water. Without water, these chemical reactions can't happen.

Living things need water because they are made of water. Most living things are 70-80% water and some organisms like the jellyfish are 95% water. In a sense, when we drink water we are replacing a part of ourselves, like replacing a brick in an old building. The reason why water is such an important part of living things probably has to do with how living things originated. One perspective is that life originated in the ocean and therefore must be made from the ocean. In other words, life must be made of water. Chemically speaking, water has a lot of useful traits for living things.

Water is a liquid that flows which means that it can transport molecules from one part of a cell to another part . It also dissolves a variety of molecules so that these molecules can interact with each other in the water. Another useful property is that water doesn’t mix with oil. This is important because oil is what forms the membrane of the cell and separates it from its surroundings. If oil mixed well with water, then fully enclosed cells could not occur in the current way. Water has so many useful properties that allow life that it would be nearly impossible to list them all here.

Water is essential to a variety of functions necessary for life. Many of the compounds that cells need to consume or eliminate are soluble in water, making water a convenient vehicle for transport of those substances. Water also has a high specific heat, meaning it takes a lot of energy to change the temperature of water. This property makes water useful for regulating temperature. Water finds yet another use in mediating many of the myriad chemical reactions which enable life, such as photosynthesis and the breakdown of energy storage molecules . All that being said, none of this is necessarily unique to water. Essentially all of these properties stem from the polarity of the water molecule, which means other polar compounds have the potential to be the basis of some form of life. One such contender is ammonia.

Every living thing as we know it require water. Water helps us deliver nutrients and molecules to our cells so that they can continue producing energy for us. It also helps us remove the bad particles from our body. Water also helps animals regulate their body temperature, like mammals (you and me!)

The complex chemical reactions required to convert sunlight or food into energy, to regulate biochemical reactions, to transport molecules, to grow, to reproduce, and essentially to perform all the chemistry of life must be done in an aqueous (in water) environment. The main reason for this is that some of the molecules involved in these processes can ionize in water, meaning that they dissolve into positive and negative species surrounded by water molecules. This makes them more reactive and lowers the activation energy for many important biochemical reactions that would be impossible outside of water.

Additionally, because the molecules are dissolved in water, they are more mobile and can diffuse, making it is easer for reactive species to come together and react to form chemical products which in turn then can diffuse to where they are needed in the cell.