For details, see the thread
Are Borates Safe to Use? The only testing with cats was the same done for dogs and rabbits for the acute oral LD
50 which is the lethal dose where 50% of the animals die. This was in the range of 250-350 mg/kg of body weight. A typical cat is usually more than 8 pounds so 3.6 kg so would have to drink (3.6*250)/50 = 18 liters for a lethal dose. Since the lethal dose for cats was similar to that of dogs, we can use the No Observed Adverse Effect Limit (NOAEL) for dogs which is 8.8 mg/kg/day which for a 3.6 kg cat is (3.6*8.8)/50 = 0.64 liters or 2.7 cups. Cats do not drink very much water as they are supposed to get more of their water requirements from wet food and there is no way they drink close to cups of pool water every day.
So your cats are probably fine. It's dogs that are more of a concern since they tend to drink a lot more (even accounting for their body weight) though even then they are not likely to drink so much as to be affected. Nevertheless, it gets close enough given intra-species variation (variation between members of the same species) that if one has a dog it's probably best to train them not to drink from the pool or to consider not using borates.
As for people, the EPA uses a Margin of Exposure (MOE) safety factor of 100 -- a factor of 10 for intra-species variation and a factor of 10 for inter-species variation. This is very conservative. With the 8.8 mg/kg/day, they assume oral exposure of 8.8/100/50 = 1.76 ml/kg of body weight. So for a 50 kg (110 pound) person this is 88 ml or 3 fluid ounces. Remember that this would have to be every day for months and even then this is with a factor of 100 safety margin and still at the No Observed Adverse Effect Limit. Without the safety margin, it's 9.3 quarts per day. So unless people drink a lot of pool water every day, it's very unlikely they are at risk. That's why the EPA set the limits where they did at 50 ppm Boron for swimming pools -- they tend to be fairly conservative and safe.
As for other chemicals in the pool, they are even safer at their levels in the pool. Nevertheless, if your pool is a salt pool with 3000 ppm salt, you wouldn't want to drink large quantities. It wouldn't kill you, but it would equal the recommended 1500 mg salt per day by drinking just half a liter (about 2 cups). Basically, pool water is not for drinking. It's for swimming.