As a general rule, you never add water directly to concentrated acid, as it might result in a powerful, exothermic reaction leading to uncontrolled splashes of concentrated acid. However, in some lab work, it’s necessary to do this, and in such cases, careful safety measures must be taken:

  1. Wear thick acid proof gloves to protect your hands.
  2. Wear safety goggles.
  3. Make sure the concentrated acid is cooled in an ice bath.
  4. Don’t add the water in a single instance, but add it slowly over several seconds.

Points 3 and 4 reduce the risk of splashing, whereas point 1 and 2 protects the one performing the lab work.