An improved chlorination system for pools, spas, potable water supplies, and the like, provides a vertically oriented electrolytic cell connected between a pump and a lightly salinated pool. The cell preferably contains a metallic electrode, such as titanium, and a precious metal coated titanium electrode, and has means for passing an electric current through the cell. The present invention further provides a novel electrode stack design, conducive for forming an efficient chlorinator comprising a plurality of interconnecting electrode stacks of separate electrical cells.