Have you ever wondered what happens to reservoir water as the seasons change?
Throughout the year, temperature shifts cause water in a reservoir to move, layer, and eventually mix. This natural seasonal cycle—called stratification and turnover—is an important part of how healthy reservoirs function.
What Happens During the Summer?
When the weather warms up, the sun heats the surface of the reservoir. The deeper water, protected from sunlight, stays cooler. It’s a bit like a layered drink: warm water on top, cool water below. This separation is known as stratification. During stratification, these layers do not mix easily. The cooler, deeper water remains isolated from the warmer water near the surface.
What Happens in the Fall?
As temperatures drop, the surface water begins to cool. Eventually, the water throughout the reservoir reaches similar temperatures. Once that happens, wind, cooler weather, and changing conditions help stir and mix the water from top to bottom. This mixing process is called reservoir turnover. There is no set date for turnover. It depends on temperature, wind, rainfall, and other local conditions. In our region, turnover typically begins in the fall as temperatures start to decline.
Why Does Turnover Matter?
Water that has been resting in deeper layers often has different characteristics than surface water. When turnover begins and those layers mix, these differences can temporarily affect overall water quality. That’s why monitoring is essential. Water Supply staff track reservoir conditions year‑round, especially during seasonal changes. Understanding turnover helps us anticipate and respond to changes before the water reaches the treatment plant.
Protecting Our Water Starts at the Source
Reservoir turnover is a normal and healthy seasonal process, not an indication that anything is wrong. By understanding how and when turnover occurs, Water Supply continues working behind the scenes to protect our community’s drinking water. Protecting our water starts long before it reaches your faucet.
