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 through the air, by rapidly moving 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 testkits measure dissolved oxygen in milligrams/litre as a concentration, using the Chemetric dissolved oxygen test. 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 extent, salinity. For example, at sea level:

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

Looking to buy our testkits in the United States?

We’ve teamed up with Chemetrics, the creators of this beautiful dissolved oxygen test, to sell our water quality testkits in the United States!

View Water Rangers testkits at Chemetrics

Water Rangers protocol

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

While a probe will give you more fine-grain results, we haven’t found inexpensive ones that we thought were as good as this test (plus, they need calibration every time you use them). When you’re recording results, you’re looking to see if results are low, medium, or high. Low oxygen might be found naturally in some ponds and bogs, but usually, low levels are a sign that you have excess nutrients in the water.

Start testing dissolved oxygen with these:

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 the sample quickly than to get exactly 25mL.
  3. IMMEDIATELY put ampoule, tip down, into the sample. Break the ampoule end off using one of the ridges at the bottom of the sample container by pressing against the ridge and pushing inward. It takes less pressure than you think!
  4. The ampoule will fill with water. Once mostly filled, remove from the sample and invert two times (watch the bubble travel up/down two 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 halfway point.
  7. Recorded your results, carefully pour water out, leaving the glass tip in your sample cup. Remove tip and used ampoule and put in a WhirlPak bag (side pocket). You can dispose of the waste in regular garbage when you return home.
  8. Pack up your kit. Do not expose the comparison chart or ampoules to light except while conducting the 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 it under the top lip first and press downward. On sunny days, find a shady spot to compare results.


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

Contributing to the community!

Water Rangers is led by community science and gets better because of the community’s input. So, if you have any questions, ideas, or notice any errors related to our tests, please tell us!