First figure out how many liters of water are left in the pool when it's 80% full: 2000L * .8 = <<2000*.8=1600>>1600 L
Now subtract that amount from the pool's total capacity to find how much water can splash out before Jim has to refill it: 2000 L - 1600 L = <<2000-1600=400>>400 L
Now multiply that amount by 1000 to convert it to milliliters: 400 L * 1000 ml/L = <<400*1000=400000>>400,000 ml
Finally, divide that amount by the amount that splashes out with each jump to find the number of jumps before pool cleaning: 400,000 ml / 400 ml/jump = <<400000/400=1000>>1000 jumps
#### 1000