A d.c. discharge which burning in open air between two flows of tap water is investigated. It appears that the discharge can be operated steady in a diffuse mode at a relatively high voltage and a low current density. Plasma parameters in the interelectrode gap are measured by means of electric probe, spectroscopic and microwave emission absorption techniques. A comparison with a theoretical calculation shows that discharge plasma is far from the thermal equilibrium and allows to determine a plasma composition. The results obtained shows that this discharge can be used for a monitoring of technical and waste water, an analysis and cleaning of waste gas flows.