Waterproof with recoating sealer applied to the interior surface of the cloth. This is usually a thinner version of urethane based seam sealer. Paint/spray it on, and let dry. You can then seal the seams with the thicker stuff.

This makes the fabric waterproof but still allows the outer surface to get soaked, sag and cling. Which makes wearing it a miserable experience. To prevent this you want a water repellant. For everyday/job use I use spray silicone because it can be spot treated and touched up quickly and easily and after a few complete coatings the silicone saturates the fabric and can compete with the higher end stuff for durability.

Essentially you spray and let hang outside to dry. At the first sign of loss of repellency I touch up the high wear spots like the shoulders and tops of the arms.

There are other repellants. The best are termed DWR, Durable Water Repellants, and they can last for months of daily use and even some washing. But these treatments are more involved to apply initially, usually you need to wash to clean, rewash with special soap to prep the fabric, wash in or spray on the treatment and, usually, air dry, and then dry in a hot drier to activate it. Some types can't be spot recoated so you have to process and retreat the entire piece.

Hint: Follow the companies directions to the letter. Slight variations and shortcuts can cripple performance.