There is a particular kind of sadness in watching a favourite walking jacket give up the ghost. It starts with a damp patch on the shoulder after a shower that would once have simply beaded off. Then a nick in the sleeve appears where you brushed a hawthorn. Then the zip starts catching, and before you know it you are standing in a shop trying to justify the price of a replacement when, with an hour of your time and a few pounds' worth of kit, the old one might have lasted another five seasons.

Outdoor clothing is not disposable, but it does need looking after. Membranes and durable water repellent finishes are consumables, not permanent fixtures. Treat them as part of the maintenance cycle, like re-waterproofing boots or cleaning your stove, and you will get years more out of every jacket you buy.

Start by understanding what has actually failed

Most jackets are not leaking. They are wetting out. That distinction matters enormously, because it determines what you do next.

A waterproof membrane — whether it is a laminated sheet or a coating — sits inside the fabric. It keeps water out and lets vapour through. On top of that sits a durable water repellent finish, usually abbreviated to DWR. When it is working, rain beads up and rolls off. When it has worn away, the outer fabric soaks up water like a sponge. The jacket becomes heavy, clammy and cold, and the membrane underneath stops breathing because it is smothered in a layer of wet cloth. You feel damp. You assume the jacket has failed. In fact, it just needs reproofing.

If water beads on the fabric but you still feel wet inside, you are overheating rather than leaking. If water beads on the fabric and you have a genuine wet patch at a seam or pocket, that is a real leak, and it needs a repair.

Cleaning the fabric gently but properly

Dirt is the enemy of waterproofing. Body oils, sun cream, mud and salt all clog the fabric and degrade the DWR. A dirty jacket will never reproof properly, so cleaning comes first.

Always read the care label inside the jacket before you do anything. It knows more than any advice column. That said, the general routine is consistent:

• Empty every pocket, unzip everything, and loosen all the drawcords and velcro cuffs.
• Brush off dried mud with a soft brush while the jacket is dry.
• Close the main zip but leave pit zips and pockets open so water can flush through.
• Wash on a gentle cycle at 30°C, using a specialist technical cleaner rather than household detergent. Regular washing powder leaves behind surfactants and optical brighteners that actively attract water and destroy the DWR. Fabric softener is worse still.
• Use a low spin or, better, no spin at all.
• Rinse twice if your machine allows it. Any residue left behind will sabotage the reproofing.

If you have no access to a machine, hand washing in a bath of cool water with a little technical cleaner works perfectly well. Agitate gently, rinse thoroughly, and do not wring the fabric.

Reproofing according to the care label

Once clean, you have two routes. Some DWR finishes can be reactivated simply by applying heat. Tumble drying on a low setting for twenty minutes, or warming the jacket with a cool iron through a cloth, often brings the repellency back without any product at all. Try this first — it costs nothing.

If that fails, you need a reproofing product. There are broadly two kinds, and choosing well matters:

• Wash-in treatments are easy but coat the whole garment, including the inner face and the lining. On a lined jacket this can reduce breathability and make the inside feel slightly tacky. They suit simple shell jackets and fleece-lined waterproofs.
• Spray-on treatments are more targeted and are usually the better choice for anything with a membrane, a liner or a soft-touch outer face. Hang the jacket, spray evenly from about 20cm, paying attention to shoulders, hood and sleeves where rain hits hardest, then let it dry.

Whichever you use, apply it to a damp jacket for the most even finish, and always follow the care label or the product instructions for drying. Many spray treatments need a warm tumble dry to cure properly and will not perform if simply left to air dry.

Repairing small tears before they spread

A two-millimetre nick is a five-minute fix. Left alone, it becomes a rip, and a rip in a membrane means a leak you cannot reproof away.

For clean, small tears in the outer fabric, a self-adhesive repair patch is the workhorse of the trade. Cut a patch with rounded corners — sharp corners peel up — and make it at least a centimetre larger than the damage on every side. Clean the area with a little alcohol, press the patch down firmly, and warm it gently with your hand or a hairdryer to help it bond.

For a clean split along a seam or a straight tear, needle and thread still have their place. Use a fine needle and polyester thread, and sew with small, close stitches, working from the inside if you can. Finish with a thin smear of seam sealant over the stitching to close the holes the needle made.

Pinhole leaks at seams, particularly on older jackets where seam tape has lifted, respond well to a flexible seam sealant applied thinly and left to cure overnight. Do not overdo it — a thick bead will crack.

Zips, velcro and the bits everyone forgets

Zips fail more often than fabric. Grit and salt jam the teeth, and a stiff zip gets forced, which bends the sliders. Clean the teeth with an old toothbrush, then run a silicone lubricant or a wax pencil along them. Never use oil, which attracts grit.

Velcro is a quiet destroyer of cuffs and waterproof fabrics. Keep the hook side clean of fluff, and when you store the jacket, fasten the cuffs so the hooks are not free to abrade the sleeves in the cupboard.

Finally, store your jacket clean, dry and on a hanger rather than stuffed in a bag. Never leave it crumpled against a hot radiator, which can delaminate the membrane. A little attention twice a year — once at the end of winter, once before the autumn — is all it takes to keep a good jacket going for a very long time.