It's best to do this after you have acquired the Infected Vision.

Look for either the "Friendly Fire" or "Projectiles" Kill Events as both have helicopters sitting next to the Event markers.

Jump into the helicopter will bring up the event requirement screen, but simply leave the event by pressing B.

With your new helicopter at your disposal, activate your Infected Vision.

Target and destroy infected water towers (around 8-10 machine-gun rounds or 1-2 non-homing missiles each) for between 8,000-15,000EP each, other helicopters (about 12-15 machine-gun rounds or around 6-9 non-homing missiles each) for about 20,000-35,000EP each, or Hives for around 30,000-40,000EP each.

The helicopter is equipped with 600 machine-gun rounds, 220 non-homing missiles, and 14 homing missiles.

Destroying 25 infected water towers before they hatch couldn't be any easier and the mass amounts of EP points you'll get from a single helicopter is a major bonus.

Remember: like my Thermobaric Tank hint, if you leave the helicopter it will vanish back to the Event marker. Also, if you destroy a Hive or Base, it will randomly vanish. I've taken out anywhere from a single Hive to 6 compounds (4 Hives and 2 Bases) before it has vanished on me. Be prepared to run just in case.