An apparatus and method for removing contaminant species from water by electrocoagulation are described. Alternating grounded, rotating, planar circular electrodes and stationary planar electrodes function as a Tesla fluid pump when placed in contact with the contaminated water, causing the water to flow between the rotating and stationary electrodes. An insoluble abrasive material introduced into the water removes scale from the electrodes while the water is pumped thereby. A direct electric current is caused to flow between each pair of rotating and stationary electrodes, thereby producing electrocoagulation of the contaminants in the water flowing therebetween. The electrocoagulated materials may be separated from the treated water by filtration or by permitting the treated water to stand for a chosen period.