I've applied just melted paraffin wax which really beads up water well but it's downside is that the treated fabric becomes pretty darn stiff at first and takes awhile to wear in. Depending on how heavy the treatment, the paraffin can also flake for awhile. The method I've used to apply just the wax is to rub the wax onto the fabric and then heat it with a hair dryer (like this).

To soften the paraffin and make it more pliable I add boiled linseed oil (boiled dries quicker than raw) about 4 floz to 1lb wax. The downsides to the addition of linseed oil is that it can lend a yellowish tint to the item being treated, but waxing fabric also darkens it substantially anyway, and the smell of linseed oil takes a few weeks to go away.

To apply I heat the wax/linseed on a candle warmer ($5 at a thrift store) and use a little cloth pad to work it onto the fabric under a heat lamp which keeps the wax molten allowing me to really work the wax in. Retreating can be time consuming but initial treatment is a serious commitment. A couple of months ago I bought a mid-length Czech military coat and it took me a total of about 9 hours to do the initial waxing. Retreating is a once a year task and it's best to do it during the summer so that you hang the treated items outdoors in the heat/sun where the treatment has a lot of time to soak in and also allow the linseed oil to dry relatively quickly.

There's quite a bit of info on the web as well as instructional videos on YouTube... good keywords are "waxed cotton", "tin cloth", "oil skin", "DIY", "reproof", "Barbour", "Filson".