Cold atmospheric plasma discharges in air above air–water surface interface and discharges inside water with injection of air bubbles, show interesting properties for water purification. Water parameters during plasma treatment get different values depending on discharge schemes. Detailed measurements of water parameters during plasma applications as pH, oxidation–reduction potential, total dissolved solids and conductivity are essential in understanding micropollutants degradation mechanisms in water. E. coli bacteria in water have been eliminated faster by plasma discharges produced in water than in air above it. Degradations of two antibiotics oxytetracycline hydrochloride (OTC) and doxycycline hyclate (DXC) in water solution are faster for plasma generated below solution surface than above it with appearance of one degradation product for OTC and two for DXC along plasma treatment time. Degradations are enhanced in the solution after 200 h following plasma treatment for the two antibiotics. H2O2 concentration can give a good indication of plasma effectiveness on different pollutants as it is a relatively stable compound. For water purification, contributions of two factors have to be identified namely water acidity with certain pH value and concentrations of reactive species generated in water. For plasma discharges inside water with air bubbles the most pronounced effect is the increasing value of H2O2 generated in water, while for plasma discharges above water the effect of water acidity induced by low pH is more dominant regarding pollutants degradations.