Shower curtains don't weigh very much, so a lightweight rod can support them. Tension rods, which are the most common type, actually consist of a pair of rods, both made from thin metal. One rod fits inside the other, and a spring inside the larger rod maintains outward tension on the ends to keep it in place. Tension rods don't always do the job, especially when you use double curtains or heavy ones. In that case, you may need to install a single wood or metal rod supported on either end by brackets screwed to the walls.
Installing and Adjusting a Tension Rod
Installing a tension rod takes just a few minutes, but before you purchase one, be sure to measure the distance between the tub alcove walls to make sure the one you buy is long enough. If the distance the rod has to span is much longer than a conventional bathtub, more than about 6 or 7 feet, consider a more heavy-duty alternative, such as a wood or metal rod supported by brackets. Long tension rods tend to sag in the middle because the metal is so thin.
You adjust the length of a tension rod by twisting one section while holding the other steady. Twist the smaller diameter rod clockwise with respect to the other one to shorten the length and counterclockwise to lengthen it. When installing the rod, adjust its length, so it almost fits inside the alcove, then insert the rod through the curtain hooks. Hold the rod in place with the curtain about an inch off the floor, then twist the smaller rod counterclockwise to lengthen it. Keep twisting after both ends have made contact with the walls until the rod has enough tension to stay in place. Give the rod a final twist through another quarter turn or more just to be sure. If you find the curtain slipping while you're showering, you can usually fix this with a bit more twisting.
Installing a Rod with Support Brackets
You can purchase chrome shower rods with decorative brackets, or you can make your own rod with a length of wooden dowel and some closet brackets. Either way, you have to cut the rod to the proper length with a hacksaw before you can install it. When cutting the rod, don't forget to allow for the thicknesses of the brackets, which usually reduces the rod length from 1/4 to 3/8 inches.
The easiest way to position the brackets, so you can mark the positions of the screw holes for pre-drilling, is to measure for one, using a tape measure. Then, hold the rod on that mark and use a level to position the other end, so you can make the mark on the other wall. Drill a pilot hole for a screw anchor on each wall, using a masonry bit if it's necessary to drill through tile. Tap an anchor into each hole, position the bracket, then drive a screw to hold it.
If the rod has decorative escutcheons, be sure to slide these onto the rod before you set it in the brackets. Once the rod is secure on the wall, you can slide these escutcheons to the ends to cover the brackets, and tighten the set screw on each one to hold it in place.