How much fizz in water carbonated with ISI whipper?
When carbonating in the ISI whipper, it is important to start with a cold liquid (or fruit, i.e. carbonated grapes).  Charge with one CO2, agitate, then slowly release the pressure so that you remove all air from the charger.  Then, charge with one or two (depending on size of ISI) CO2 charges to fully carbonate.  If you leave out the first step you are simply compressing trapped air, rather than dissolving CO2 into your product.