A mat for removable installation on the floor surface of a vehicle foot well has at least one through-hole for receiving a mat retention device. At least one endless elastomeric sealing member extends radially inwardly from a general sidewall surface of the through-hole. A grommet for the through-hole includes a bottom grommet and a cap. An outer sealing surface of the grommet compresses the elastomeric sealing member of the through-hole, thereby creating an impermeable barrier to water incident on an upper surface of the mat body. The mat body may have an endless ridge on its upper surface that is radially outwardly spaced from the through-hole and that is compressibly engaged by a lower surface of a cap retention flange.