Which type of water can contain more Dissolved Oxygen (DO)?

Cold water is capable of holding more dissolved oxygen (DO) than warm water or other types of water. This is primarily due to the physical properties of gases in liquids; as temperature decreases, gases become more soluble. In cold water, the kinetic energy of the water molecules is lower, which allows more oxygen molecules to remain integrated in the water.

In comparison, warm water has higher kinetic energy, which causes the gas molecules to escape more readily into the atmosphere, resulting in lower levels of dissolved oxygen. Saltwater can have lower concentrations of DO compared to freshwater due to the presence of salt ions, which can interfere with the solubility of gases. Polluted water typically contains organic matter that consumes oxygen through biological processes, further reducing DO levels.

Thus, cold water is the most effective medium for maintaining higher concentrations of dissolved oxygen, making it essential for aquatic life, particularly in cold environments or during cooler seasons.