Health of Water System

By Melany Contreras and Caleb Medlin

Health of Water System

People don't understand how important water quality is to their life. water quality is vital to the Earth's ecosystem and its organisms.

Dissolved Oxygen

Oxygen is dissolved in water. This is known as dissolved oxygen(DO). If the DO level in freshwater is below 4.0 mg/L, can cause stress and possibly death for organisms that live in the water. Pollutants such as sewage, fertilizer runoff, and animal waste can decrease DO levels in water.


Temperature can affect the DO level of water. Cold water holds more oxygen than warm water does. Nuclear power plants that use water as their cooling agent can increase the temperature of water. This increase in water temperature is known as thermal pollution which causes a decrease in DO levels in water.

(Picture below)Fish die-off in Brazil due to thermal pollution. Thermal pollution lowered DO levels in the water, causing a mass number of fish to die.


Nitrates are compounds of nitrogen and oxygen that are naturally occuring. Small amounts of nitrate levels in water is normal. However, if the nitrate levels in water are elevated, it can be harmful to organisms. An extra amount of nitrates in water can also decrease DO levels. Animal waste or fertilizers that seep into the groundwater can cause nitrate pollution.


The pH of water identifies the acid/base balance. Healthy water system ranges from 6.5 to 8.5. If the water is within the range, chemicals can be dissolved as nutrients. However, lower or higher pH may disrupt the availability of nutrients in a water system.


Turbidity is a measure of the concentrartion of particles suspended in water. High turbidity reduces light penetration and visibility in the water. Suspended sediments, wastewater discharge from industry, and phytoplankton (at times of abnormally high concentrations) are all a common source of turbidity. A lack of light negatively affects the health of aqauatic organisms and reduces photosynthesis.

Biological Indicators of Water Quality

Scientists use a variety of aquatic plants and animals as indicators of water quality. Important indicators are fishes. Fishes live in water their entire life and respond to chemical, physical, and biological changes in their environment in characteristic ways. Aquatic plants, aquatic insects, mussels, leeches, and worms are other good indicators of water quality.