Water Quality, Dissolved Oxygen, and Phosphorous

Activity Source: 

Source: American Association of Petroleum Geologists.
Adapted with permission.

Tap water from the kitchen has very different properties from water in a stream or a pond, even if they might appear similar. Water quality refers to the physical and chemical properties of water
that make it suitable for a particular use based on biological, physical, and chemical characteristics. A fish might live in sedimentrich water at the bottom of a lake, but you would not want to drink it!

For this activity you will need to buy a dissolved oxygen kit and a phosphorous soil testing kit to investigate two kinds of water quality. Check the packet to make sure you have enough for three water tests and two soil tests per student or per group.


• Home aquarium dissolved oxygen testing kit (from local pet store)
• Water from a tap/pond/stream
• Garden soil testing kit
• Soil sample/fertilizer
• Safety gloves
• Goggles
• Measuring cup


You will investigate two kinds of water quality.

Dissolved oxygen: A small amount of oxygen, up to about 10 molecules of oxygen per million of water, is actually dissolved in water. It is used by all kinds of aquatic life for respiration. Dissolved oxygen is transferred from the atmosphere or groundwater into streams and ponds. The amount of dissolved oxygen (in ppm or mg/L) is an indicator of the “health” of lakes and streams. When organic matter decays in water, it uses up dissolved oxygen, which can become depleted, affecting aquatic life.

Design an investigation to measure the amount of dissolved oxygen in tap water, pond water, and stream water.

  1. Read the steps on the dissolved oxygen test kit. Pay attention to the safety instructions. Make a note of the sample size and how to handle it safely.
  2. Design a method to compare the amount of dissolved oxygen for the samples.
  3. Before you begin, seek approval of your approach from an adult.
  4. After approval, put on your gloves and goggles. Follow your method for each sample. Record the results.
  5. Which environment had the most dissolved oxygen, and which had the least? Explain why.
  6. Research the dissolved oxygen requirements for local aquatic life. How healthy is your local pond and stream?

Phosphorous is an essential element for plant life. It is also a common ingredient in fertilizer because it helps plants to grow. Phosphorus gets into water from sewage and industrial waste in urban and agricultural environments. Soil erosion transfers phosphorous to streams and ponds. Increased phosphorous in streams speeds up plant growth but also algae. After they die, the bacteria that decompose them use up dissolved oxygen in the water which can eventually create dead zones where fish cannot survive.

Design an investigation to compare the amount of phosphorous in untreated soil to a sample of soil thar contains fertilizer.

        7. Read the steps of the phosphorous test kit. Pay attention to the safety instructions.
        8. Design a method to compare the concentration of phosphorous in two soil samples. Seek approval of your approach from an adult.
        9. After approval, put on your gloves and goggles. Follow your method for each sample. Record the results.
        10. How did the samples compare?
        11. How could you reduce the transfer of phosphorous into streams as a result of soil erosion by rain.