Water Quality MAIN Iowa Public Television
Search Help Teacher Resources Contact Us
Web Sites Glossary Careers Explore More Project
Uses Pollutants Issues Viewpoints Water In-Depth Features
  What's in the water


Water is amazing! In fact, you can't live without it. Water's special molecular structure allows it to form bonds with any positively or negatively charged atom. Water is a universal solvent meaning it dissolves other substances and transports both good and bad molecules. So, what's in the water? A lot!
Molecular Structure
Two hydrogen (H) atoms attach to one oxygen (O) atom to form a water molecule (H2O.) Each hydrogen atom forms a covalent bond with the oxygen atom--they share a pair of electrons. Oxygen has an extra pair of electrons that are not shared. The extra electrons are on the side away from the hydrogen atoms . This makes the oxygen side of a water molecule negative. The hydrogen side is positive. Water's polarity means it dissolves most everything--good and bad, positive and negative.
Water can exist in three states.

Ordered molecular state

Water as a Solid
Water can be a solid like ice or snow. Frozen water is in an ordered molecular state. This means all atoms are bonded. There are no or few atoms free to bond with other atoms. This makes it difficult for the atoms within polluting substances bond with the atoms within water. Therefore, polluting substances are not dissolved by water when it's in a frozen or ordered molecular state.

The next time you put an ice cube in a glass of soda, notice the soda doesn't "mix" with the solid ice cube. The water remains solid until temperature forces the water to change states. The ice melts. The soda mixes with water only after the ice, solid water, melts into a liquid state.

Semi-ordered molecular structure

Water as a Liquid
Water can be a liquid like you would find in a flowing river, a calm lake, or even in a glass for drinking. Water as a liquid is in a semi-ordered molecular structure. This means some water molecules have atoms available to bond with the atoms of other substances. Water as a liquid can dissolve these substances. If the substances contain pollution, the result is a solution made up of pollution and water.

Water as a liquid gives free transportation to pollution. Take a spoonful of baking soda and empty it onto the counter. It's confined to one place. But if you add that same spoonful to a glass of water and then pour it onto the counter, the baking soda gets transported all over the place. It may even run off the counter onto the floor where you definitely don't want it. Imagine it you added something worse than mere baking soda!

random molecular structure

Water as a Gas
Water can even be a gas which is the water vapor you can see when boiling water. Water vapor is in a random molecular structure. Water vapor is a gas diffused in the air. Its molecules are distributed randomly or "spread out." In this state, all of the water molecule atoms are available for bonding with other substances. However, like in its frozen state it does little bonding. Why? Because the molecules are distributed so randomly that there is less of a chance of water molecules and other substances finding each other. But they do sometimes bond.
Sometimes the pollution is already in water and vapor merely transports it up to the clouds.

Check out the water cycle section to see how water moves from land to air and back again.

Bonds, cohesion, adhesion, and dissolved oxygen
Water's atomic structure is unique and simple. A water molecule is made up of just three parts: an oxygen atom and two hydrogen atoms. This structure is unique because it produces electrochemical properties. The structure makes a water molecule have a positive side and a negative side. Water is actively attracted to other molecules. At the same time, other molecules are attracted to water molecules.

Universal solvent
Because water molecules have a positive side and a negative side, any atom with a positive or negative charge can bond with it. In fact, water is a universal solvent. This means water can combine with other chemicals to form a solution. Chemical nutrients can then be carried as a solution through runoff into surface water, or infiltrate ground water.

NaCl (Salt crystal)

Saline Solution

The pH of water molecules is not basic (alkaline) or acidic. It is neutral until water dissolves other substances. Since water can bond with just about anything, you rarely get pure water, or the chemical state H2O, without other bonded molecules of something else. So water usually picks up other molecules, like carbon dioxide for example, as it travels through the water cycle.

Any substance with as pH less than 7 is considered acidic. Rain has a pH of 5.6 which is considered "normal." However, sometimes rain is far more acidic. When rain has a lower pH than 5.6 it is called "acid rain." Water vapor as it reaches the clouds can come into any number of pollutants we put into the air such as carbon dioxide (CO2), sulfur dioxide (SO2), and nitrogen oxides (NO1-X). The water vapor attracts the positive hydrogen ions of these pollutive substances to form acid rain. The pollution comes from many sources including

Minerals, sediment, and additives
So what ends up in the water, what bonds with water molecules, as water travels through the water cycle? Minerals, sediment, and additives are on the "what's in the water" list.

Water's unique structure allows it to create strong bonds. These bonds create density. Therefore, water can transport heavy minerals like salt, calcium, potassium, or zinc. They transport these minerals not only through rivers and over land, but through your body as well.


Unfortunately, sediment can be transported as well. Sediment is usually in the form of dirt and it is not wanted in our waterways.


Additives used to purify drinking water, like chlorine, travel with water from a processing plant to your faucet. Sometimes other additives like fluoride are introduced into a communities drinking water for the purpose of reducing tooth decay.

Explore More: Water Quality
Copyright 2004, Iowa Public Television
The Explore More project is supported by funds from the
Roy J. Carver Charitable Trust
and the USDE Star Schools Program.