Perhaps, but that's just as well. At least for dogs, the No Observed Adverse Affect Level (NOAEL) is 8.8 mg/kg/day so for a 3.5 kg (7.7 pound) cat this is 30.8 mg or 0.616 liters (2.6 cups) of 50 ppm borate water per day every day. So while safe (cats don't drink that much), it's just as well the cat not drink from the pool.