Yes, you can. Just make sure that you water proof the window area well and then use an epoxy grout like Laticrete's Spectraloc grout. It never needs sealing, will not mold or mildew like the standard grouts. Also caulk next to window. Another tip- Make sure to slant the sill slightly to allow water to run off. I also would recommend the shower high enough for privacy and to keep water spray onto it.