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In a stratified reservoir, the best quality water is typically found in the epilimnion. The epilimnion is the upper layer of water that is warmed by sunlight and is well-mixed due to wind action. This layer allows for higher levels of dissolved oxygen, which is essential for supporting aquatic life. Additionally, the conditions in the epilimnion are favorable for photosynthesis, contributing to higher water quality.

The hypolimnion, being the deepest layer, is usually colder, denser, and can become depleted of oxygen, especially in the absence of mixing during stratification. The metalimnion, also known as the thermocline, is characterized by a rapid change in temperature and lacks the consistent quality and oxygen levels found in the epilimnion. The thermal stratification zone corresponds to the general concept of layering in a stratified body of water but does not pinpoint the best quality water found in the epilimnion specifically.

Thus, the epilimnion is where one would find the best quality water in a stratified reservoir, due to its warmer temperatures, higher oxygen levels, and favorable conditions for life compared to the other layers.