The effects flow rates of gas, liquid, or gas composition, in non-thermal plasma (NTP) electrical discharge reactors, on nitrates and hydrogen peroxide generation in water, have been studied. The reactor set up consists of two stainless steel tubes placed in a glass tube. The effects of successive passing the same sample water through one, two or three identical columns of NTP electrical discharge, were determined by serial connection of several similar reactors (up to three). In all cases, the efficiency of the nitrates and hydrogen peroxide production in treated water in the NTP reactor(s) have been also calculated.