Oxygen in Drinking Water Supply
The Presence of Oxygen in Drinking Water Systems
Rainwater, frequently considered one of the purest water sources, possesses the ability to absorb various atmospheric gases such as carbon dioxide, oxygen, nitrogen dioxide, and sulfur dioxide. As it falls, it also captures soot and other minute particles. Upon hitting the ground, rainwater is nearly 100% pure. Among the gases absorbed, oxygen plays a crucial role. The oxygen dissolved in rainwater differs from the oxygen within the water molecule itself. This dissolved oxygen is present in all rainwater and surface water sources due to their interaction with the atmosphere. Aquatic life relies on it, yet it is rare in water, with an oxygen concentration of only 0.001% compared to 21% in air. The concentration of dissolved oxygen in water depends on several factors:
- Water aeration: High-pressure conditions allow for significant oxygen dissolution in water. When pressure is reduced, the gas is released proportionally (as per Henry’s Law*).
- Water’s mineral content: Water with a higher mineral content has a decreased ability to dissolve oxygen, with distilled water being an exception as it can absorb more oxygen than mineral-rich well water. Seawater also contains less dissolved oxygen than freshwater due to its mineral content.
- Excessive nutrients: These can lead to "algal bloom," excessive algae growth that blocks sunlight and reduces dissolved oxygen, causing plant death and subsequent oxygen reduction as decay occurs.
Well water typically contains lower levels of dissolved oxygen than surface water, and in deep wells, oxygen may be completely absent. However, a study published in Science Magazine on June 11, 1982, challenged the belief that soil and aquifer reactions quickly deplete oxygen, revealing that 2 to 8 milligrams per liter of dissolved oxygen can persist in deep aquifers in certain regions.
Oxygen affects the taste of water, making a small amount desirable in drinking water. The "flat" taste of water can be improved by reintroducing oxygen through shaking. However, dissolved oxygen can cause corrosion in water supplies, particularly when water is heated.
Industrial processes utilize chemicals such as sodium sulfite to remove oxygen from water. For domestic use, polyphosphates are commonly used to coat water pipes and prevent oxygen contact with metal.
Henry’s Law, established by William Henry, pertains to the pressure-dependent dissolution of gases in liquids, stating that the weight of dissolved gas is proportional to pressure, given constant temperature.
Human activities, including damming, waste disposal, and the use of fertilizers and agricultural waste, affect dissolved oxygen levels. Dams decrease water flow and aeration, while waste introduces bacteria that consume dissolved oxygen. Fertilizers cause algae blooms, which reduce sunlight and lead to lower oxygen levels.
We must endeavor to prevent these occurrences, respect our environment, and take necessary precautions. Individually, we have the power to make a positive impact.