Traditional leather boots, when well waxed, tend to give a good level of proofing against water penetration provided that there are no areas of poor or damaged stitching to let in water.

Weatherproofing your leather shoes will help to protect them from water and other elements that can ruin the finish and shorten the life of your shoes.
Consult the manufacturer for the proper products to put on the boots for waterproofing. Waterproof the boots before you use them for the first time. Some people advocate waxes, silicones or oil based products for leather boots.

The thought is that wax or silicone based products will ruin the natural properties of leather and shorten the life of the boot. There is a difference between a paste wax and water based liquid wax. Some boots require a water based wax while other boots require the paste wax. Whatever waterproofing is used, consult with the manufacturer for sure.

Always make sure the attachment area where the boot and the sole meet have enough waterproofing. A very soft toothbrush or Q-tips will help get into those tough boot areas. Whatever waterproof product is chosen, use a reputable brand product for those expensive boots.

There are a large variety of waterproofing products available for smooth leather, suede or nubuck.