The typical problem of "cattle eating grass" is difficult to keep popping up in the water.

Set the water pump 1 hour and pump 1 serving of water.

Then 10 pump will pump out 8* 10* 1=80 copies in 8 hours.

8 pumps 12 hour pumping 8* 12* 1=96 copies.

Then 96-80= 16 parts of water is 12-8=4 hours of fresh water, and the output of fresh water per hour is 16÷4=4 parts.

So the original water in the pool is 80-8*4=48 parts.

Because one water pump pumps 0 hours 1 serving of water, we use 4 of the 6 pumps to pump 4 portions of fresh water every hour, and the remaining 6-4=2 pumps 48 portions of raw water, so it takes 48÷2=24 hours.