Fluid purification or treatment apparatus (10) for treating or purifying contaminated liquids such as water which includes at least one upright elongated primary treatment chamber (11) having an inlet (14) for fluid to be treated at an upper end of the chamber (11) such that fluid flows downwardly through the chamber (11) and means (20 or 24) for introducing a sterilizing agent such as ozone or ozone enriched air into a lower end of the chamber (11) for bubbling upwardly through liquid flowing downwardly through the chamber (11), means (16) at the upper end of the chamber (11) for removing waste and an ultraviolet lamp (29) for UV treatment of the liquid, the ultraviolet lamp (29) being located in a separate chamber (12) connected to the primary treatment chamber (11) or within the primary treatment chamber (11). A plurality of chambers (11) and (12) may be provided for multiple treatment of the liquid.