A dirty shell is a leaky shell. The waterproof membrane breathes through microscopic pores, and body oils, sweat and grime clog them — which is what makes an old jacket feel clammy inside and wet out on the surface. Washing a technical shell is maintenance, not just cleaning.
Use tech wash, never normal detergent. Standard detergents and, worse, fabric softener leave a residue that attracts water and kills breathability. Wash with a dedicated tech-wash on a gentle cycle, on its own, and rinse thoroughly.
Heat reactivates the water repellency. The DWR finish on the outer face is what makes rain bead and roll off. A cool tumble dry — or a warm iron through a cloth — reactivates it after washing and buys you a good while longer.
Re-proof when water stops beading. The day rain soaks into the outer fabric instead of beading, the DWR is spent. Clean the jacket, then apply a wash-in or spray-on proofer and heat-set it per the bottle. Done once or twice a year, a good shell stays genuinely waterproof for many seasons.