First find the number of water breaks James takes: 240 minutes / 20 minutes/water break = <<240/20=12>>12 water breaks
Then find the number of sitting breaks James takes: 240 minutes / 120 minutes/sitting break = <<240/120=2>>2 sitting breaks
Then subtract the number of sitting breaks from the number of water breaks to find the difference: 12 breaks - 2 breaks = <<12-2=10>>10 breaks
#### 10