A process for improving a liquid carrying system comprising physically disrupting a biofilm on interior surfaces of the liquid carrying system and then providing molecular iodine onto the disrupted biofilm in a concentration in aqueous material onto the biofilm of at least 10 parts per million. The reactants may be provided before physical disruption also. The molecular iodine may be added in gaseous or liquid or solid state, and may be formed in situ in the interior of the liquid carrier system using available or added water in the reaction.
