What device must be activated before opening the pool each day?

The correct answer is the test-buttons for ground current leakage. This device plays a crucial role in ensuring the safety of both staff and patrons who use the pool facilities. Ground current leakage can pose serious electrical hazards, particularly near water. By activating the test-buttons prior to opening the pool, staff can confirm that the electrical systems in and around the pool are functioning correctly and are safe for use. This is a critical step in preventing accidents related to electrical faults in a wet environment.

In contrast, while the water filtration system is essential for maintaining clean and safe pool water, it does not directly ensure the immediate safety of individuals entering the pool area. The back-up power generator, although important for maintaining operations during power outages, is not a daily requirement for pool safety at opening. Swimming aids, while useful for enhancing the swimming experience, do not pertain to the safety checks needed before opening the pool.