Tennessee Wastewater Operator Practice Exam

At what temperature does water achieve maximum density?

1. 0 C

2. 4 C

3. 10 C

4. 20 C

The correct answer is: 4 C

Water reaches its maximum density at 4 degrees Celsius. This unique property of water is crucial for understanding aquatic ecosystems and the behavior of lakes and ponds. As water cools down from higher temperatures, it becomes denser and sinks. However, when it reaches about 4 degrees Celsius, it is at its maximum density. If water cools further to 0 degrees Celsius (the freezing point), it starts to expand, making it less dense than the water at 4 degrees Celsius. This phenomenon explains why ice floats on water. During the winter, when lakes cool, the densest water (at 4 degrees Celsius) stays near the bottom, allowing the surface ice to insulate the water below and creating a habitat for aquatic life during cold periods. Understanding this temperature is fundamental for wastewater operators, as it can impact process operations such as aeration and mixing.