PETER THOMAS ROTH To use Peter Thomas Roth Water Drench Serum , start with a clean and dry face. Take a small amount of serum onto your fingertips and gently massage it into your skin, starting at the center of your face and working outward. Allow the serum to fully absorb into your skin before applying any other products. Once the Peter Thomas Roth Water Drench Serum has absorbed, follow with your regular moisturizer. Shower Gels