In order to deal with drinking water quality crisis, from the view of flexible construction of water supply system, the paper proposes and designs a membrane water treatment facility which considering the two different needs in flat situations and in risk situation in one package. In technological aspects, according to the needs of the direct drinking water in the normal time, a stable membrane filtration process using municipal water as raw water is established to ensure the filtered water reaches the direct drinking water quality standards (CJ94-2005). At the same time, according to the basic domestic water needs in crisis times, a "pre-treatment + MF" process using the contingency reserve source water as raw water is established to ensure the filtered water reaches the filter drinking water standard (GB5749-2006). In equipment, a dual-use water production equipment is designed which can reach the usual needs of drinking water and the crisis needs of drinking water through the reasonable assembling. Experiments, which takes municipal water as raw water for usual and take manufacture Lake of the new campus of Tianjin University’s water for risk separately, show that the proposed facility realize the design function.