Which tool is essential for maintaining the proper water level in a pool?

Maintaining the proper water level in a pool is crucial for its overall health, safety, and functionality. A water level gauge or float valve system is designed specifically for this purpose. It allows for continuous monitoring of the water level and automatically fills the pool when it dips below the intended level. This is particularly important since an improper water level can lead to equipment damage, ineffective skimming, and can affect the chemical balance of the pool.

On the other hand, although the thermometer is useful for measuring water temperature, it does not contribute to managing the water level. Similarly, while a chemical testing kit is essential for ensuring the water chemistry is balanced, it does not address the water level itself. Lastly, a skimmer net is useful for removing debris from the surface of the water but does not play a role in managing or maintaining the water level. Thus, the water level gauge or float valve system is the only tool that directly ensures that the pool maintains its optimal water level.