To ensure your cooling towers are working at optimal efficiency:
Check cooling tower fills for any choking of fills
Check operation of fan for sufficient air flow (use Guidewheel to set baseline)
Ensure filtration system is effectively removing dissolved solids
If everything checks out, you can use Guidewheel Calculations (you can also use Groups if you have multiple cooling towers) to determine a baseline for efficient consumption from which increases will indicate a need for intervention.
(Note: In the image above, you can clearly denote that there was a day with excessive consumption, which is unusual when looking at the other days. Therefore, you may want to investigate that day's operations to learn more about what caused the increase.)