A dialysis system is disclosed for treatment of a first fluid with dialysis fluid, the dialysis fluid being a mixture of water and dialysis concentrate. The system comprises a dialyzer, a source of water, a source of dialysis concentrate, first and second fluid conducting means communicating with the sources of water and dialysis concentrate, pump means associated with the first and second fluid conducting means, and third fluid conducting means for conducting fluid from the pump means to the dialyzer. The pump means serves to draw water and dialysis concentrate through the first and second fluid conducting means respectively, and to mix the water and dialysis concentrate so that a mixture of water and dialysis concentrate is conducted through the third fluid conducting means.