Dissolved oxygen

What is dissolved oxygen?

This is the amount of gaseous oxygen dissolved in the water. Oxygen gets into the water in various ways, including absorbing it from the atmosphere, by rapid movement of the water, or as a product of photosynthesis.

Why is dissolved oxygen important in water?

Oxygen is what gives the water life! Fish and plants depend on certain levels of oxygen to survive.

What does a dissolved oxygen measurement mean?

Water Rangers test kits measure dissolved oxygen in milligrams/litre — as a concentration. The concentration refers to the amount of oxygen that is dissolved in every litre of water.

  • 0-2 mg/L: not enough oxygen to support life
  • 2-4 mg/L: only a few fish and aquatic insects can survive
  • 4-7 mg/L: good for many aquatic animals, low for cold water fish
  • 7-11 mg/L: very good for most stream fish

Dissolved oxygen can also be measured as a percentage. The percentage refers to the saturation level of oxygen in the water. The key factors in determining saturation are temperature, barometric pressure, altitude, and to a lesser extend salinity. For example, at sea level:

  • 100% saturation at 25℃ = 8.26 mg/L
  • 100% saturation at 0℃ = 14.6mg/L

Water Rangers Protocol

We use the Chemetrics dissolved oxygen testkit because it is the most user friendly to conduct (no measuring chemicals) and easier to interpret than other tests we’ve tried.

The inexpensive probes that we’ve tried were finicky and inaccurate (even with proper calibration). Professional probes will give you more fine-grain results, but they’re thousands of dollars and require calibration really often.

We’ve compared this kit to professional probes with great results. However, some people still find interpretation difficult. We are currently seeking funding that will use your phone camera to interpret results. Until then, follow the protocol and confirm results by comparing with a friend!

Learn more with this video demonstration.


This device has been compared to professional probes very good results.

How to test.

1. Take out an ampoule and your sample cup. Notice the ridges in the bottom. Notice the white tip on the ampoule. This is a weak point in the glass.

2. Take a water sample as far below the surface as you can reach. Do not shake. It is more important to get sample quickly than to get exactly 25mL.

3. IMMEDIATELY put ampoule, tip down, into sample. Break ampoule end off using one of the ridges at the bottom of the sample container by pressing against ridge and pushing inward. It takes less pressure than you think!

4. Ampoule will fill with water. Once mostly filled, remove from sample and invert two times (watch the bubble travel up/down 2 times).

5. Hold tip facing upwards for 2-minutes (sand timer/stopwatch).

6. Take out your comparison chart. Place the ampoule flat between the comparison chart until you and your testing companion agree on the reading. If it’s between two values, take the half-way point.

7. Recorded your results, carefully pour water out, leaving glass tip in your sample cup. Remove tip and used ampoule and put in a WhirlPak bag (side pocket). Dispose in regular garbage when you return home.

6. Pack up your kit. Do not expose comparison chart or ampoules to light except while conducting test since the dye is affected by sunlight.

Make sure you take out your comparison chart. Pull from the bottom. To put it back in, position under the top lip first and press downward. On sunny days, find a shady spot to compare results.

How to test

The dissolved oxygen test with the CHEMetrics kit

Start testing dissolved oxygen with these:

Contributing to the community!

Water Rangers is citizen-scientist led. So, if you have any questions, ideas, or notice any errors related to our tests, please tell us!