Oxygen’s Role in Water Supply: A Comprehensive Analysis

The Purity of Rainwater

Rainwater, often considered one of the purest forms of water, is derived directly from atmospheric sources. As it descends, it absorbs various gases including carbon dioxide, oxygen, nitrogen dioxide, and sulfur dioxide. Additionally, it captures soot and other microscopic particles. Remarkably, rainwater is nearly 100% pure before it touches the ground.

Dissolved Oxygen in Rainwater

Of the gases absorbed, oxygen is particularly significant. Dissolved oxygen, distinct from the oxygen within the water molecule (H2O), is crucial for aquatic life. All rainwater and surface water supplies contain dissolved oxygen due to atmospheric contact. Unfortunately, despite air containing 21% oxygen, water only retains 0.001% of it.

Factors Affecting Dissolved Oxygen

Several factors influence the amount of dissolved oxygen in water:
– **Aeration of Water**: High-pressure conditions dissolve more oxygen in water. When pressure is reduced, the gas escapes proportionally, as per Henry’s Law.
– **Mineral Content**: Water with higher mineral content, like seawater, holds less dissolved oxygen than freshwater with lower mineral content.
– **Excess Nutrients**: Nutrient-rich waters often experience “algal blooms,” which reduce sunlight penetration and dissolved oxygen levels.

Well Water vs. Surface Water

Well waters typically contain less dissolved oxygen than surface supplies, with deep wells potentially lacking any gas. However, a study in Science Magazine (June 11, 1982) revealed that some deep aquifers in Nevada, Arizona, and the hot springs of the Appalachians and Arkansas contain 2 to 8 milligrams per liter of dissolved oxygen, despite being thousands of years old.

Oxygen and Water Taste

Oxygen contributes to the taste of water, making it more appealing. The “flat” taste of water left open for some time can be improved by reintroducing oxygen through shaking. However, this beneficial element also poses challenges.

Corrosion and Oxygen

Dissolved oxygen can cause corrosion in household water supplies. While it has minimal effect on cold water, heating water can exacerbate corrosion issues.

Chemical Treatments

Chemicals like sodium sulfite (Na2SO3) are used in industrial settings to remove oxygen from water. For household purposes, polyphosphates are commonly used to coat water lines and protect them from oxygen contact.

Henry’s Law and Its Implications

Henry’s Law, formulated by English chemist William Henry, describes the relationship between gas solubility and pressure. It states that the amount of gas that dissolves in a liquid is directly proportional to the pressure, assuming constant temperature.

Human Impact on Dissolved Oxygen

Human activities significantly influence dissolved oxygen levels:
– **Dams**: Slowing water flow reduces aeration and increases temperature, affecting oxygen levels.
– **Human Waste**: Carrying oxygen-consuming bacteria, raw sewage can deplete dissolved oxygen in waterways.
– **Fertilizers**: Cause algal blooms, reducing sunlight and dissolved oxygen.

Environmental Stewardship

It’s crucial to respect and care for our environment. Preventing pollution and managing resources can make a significant difference. Let’s stay positive and take action to protect our water supplies and the life they support.

By understanding and addressing these factors, we can ensure a sustainable water supply rich in dissolved oxygen, essential for both human consumption and aquatic ecosystems.