A modular fluid containment system formed of a plurality of fluid containment units and interconnecting channels. The containment units and channels may be comprised of panel units made of flexible non-porous material.The system includes brace members along selected edges of the containment units and panel units which are operative between an operative position in which the edges of the flexible material forming the containment units and panel units are held in an upright position forming side walls defining a containment or channel area and an inoperative position in which the flexible material is allowed to lie along a single plane in flat or folded condition. Connectors are provided along selected edges of the panel units to interconnect the panel units into desired configurations forming the containment system of desired shape and size.