Your concrete basin may be leaking, but there’s no way you can take it down to do any repairs. The whole plant is dependent on the cooling tower running. If you were to coat the inside you’d have to have several days to prep and coat and then you’d have to let the new coating cure before filling the basin. That could be days or even a week.
But, if you could apply a coating that required minimal prep and could be applied to the wet concrete, you’d have time for that. With the advancements of cement chemistry and the variety of additives used in products these days, cement-based coatings are a real option for this application. Flexible cement waterproofing slurries can bridge cracks in the existing concrete. They are easy to apply and take little to no additional equipment. These products can resist up to 160 ft of water pressure and have very good adhesion to concrete.