Brønsted-Lowry acid is a specie which tends to donate H⁺, while Brønsted-Lowry base is a specie which tends to accepts H⁺. In Given compounds H₂O is a compound which can act as both acid and base.
As a Acid:
When H₂O is reacted with strong base it acts as a acid, i.e donates H⁺ and forms OH⁻.
Base + H₂O → [Base-H]⁺ + OH⁻
As a Base:
When H₂O is reacted with strong acid it accepts H⁺ and forms H₃O⁺ (Hydronium Ion), i.e.
Acid-H + H₂O → [Acid]⁻ + H₃O⁺
