Usually you let the water UNDER the plastic do what it wants to do. If it's always 'standing' under the plastic, you need to look a bit further-and-wide as to the souce of the problem. Usually, it's due to missing or incorrectly hung gutters, downspouts that drain water at the foundation (vs. 3' away, minimum), missing gutters, a landscape the slopes towards the foundation instead of away from the foundation. Use 6 mil plastic and lay gravel or pressure-treated lumber all around the edges. Just enough to keep the edges down, and from curling up.
Again, your 'bandaid' on the problem may not be enough. Look further to potentially reduce your water-source dramatically. My best to ya and hope this helps.