Not what it's meant for, I guess, but it's not very strong at chemistry ;-)

  salt - chlorine + potassium = sodium
  chlorine + sodium = rubidium
  water - hydrogen = tap water

It also has some other interesting outputs:

  woman + man = adult female body (already reported by someone else)
  man - hand = woman
  woman - hand = businesswoman
  businessman - male + female = industrialist
  telephone + antenna = television equipment
  olive oil - oil = hearth money