Descaling is the highest-return five minutes in shower maintenance, and the one most often done badly. Soak too briefly and nothing happens; soak the wrong material too long and you dull the finish. The variables are acid, concentration, time and temperature — and only two of them really matter.
What scale actually is
Hard water carries dissolved calcium and magnesium bicarbonate. When the water evaporates from a nozzle orifice — which happens every time you finish a shower — those minerals precipitate out as calcium carbonate. It is the same chemistry as kettle fur, and it is stubborn in a very specific way: it bonds to the surface and then builds on itself.
That is why one blocked nozzle becomes five. The first crust creates a rough surface that holds water longer, which deposits more scale, which holds more water. Descaling breaks the cycle by dissolving the carbonate back into solution.
The chemistry, in one paragraph
Calcium carbonate is a base. Any mild acid converts it into a soluble salt, water and carbon dioxide — which is why a descaler fizzes on contact. Vinegar is dilute acetic acid at about 5%. Citric acid is a solid that you dissolve in water, typically one tablespoon per litre. Proprietary descalers such as CLR use stronger acids, usually lactic or phosphoric, and work faster at the cost of being less forgiving.
Scrape a little of the white deposit into a cup and add vinegar. If it bubbles, it is carbonate scale and acid will work. If it does nothing, the deposit may be silica, iron or sealant residue, and acid will not touch it.
White vinegar: the default
Vinegar is cheap, available everywhere, and safe for chrome, brass, plastic and most rubber. It is also slow — which is why the bag-over-the-head method is always described as "overnight". Four hours is the practical minimum for moderate scale; eight to twelve is better and does no harm to chrome.
Its weaknesses are the smell, which lingers in a small bathroom, and its effect on some natural stones and on aluminium. Neither is usually present in a shower head, but both matter if you are soaking a faceplate on a marble sill.
"Take some vinegar or CLR in a plastic bag and tie the bag over the shower head so the jets are submerged, and let it sit overnight."
Citric acid: faster, quieter
Citric acid does the same job in a third of the time and leaves no smell. A tablespoon per litre of warm — not hot — water is enough. It is the better choice if the bathroom is small, if anyone in the house objects to vinegar, or if you descale monthly and want the job over with.
It is slightly more aggressive on plated finishes at high concentration, so measure rather than pouring. Undissolved crystals sitting against a chrome surface can leave a dull spot.
Proprietary descalers
Products like CLR work in fifteen to thirty minutes. They are useful when a head has been neglected for years, and unnecessary for routine maintenance. Two rules: follow the dilution on the label, and never mix a descaler with bleach or with another cleaner. Acid plus hypochlorite releases chlorine gas, which is genuinely dangerous in a bathroom.
Never mix cleanersAcid descalers and chlorine bleach produce chlorine gas. Rinse the head thoroughly before switching products, and ventilate the room whenever you use a strong descaler.
How long to soak
| Severity | What it looks like | Vinegar | Citric acid |
|---|---|---|---|
| Light | Hazy film, all nozzles still flowing | 2 hours | 1 hour |
| Moderate | White rings, some jets spraying sideways | 4–6 hours | 2 hours |
| Heavy | Crusted face, several nozzles dead | 8–12 hours | 4 hours |
| Neglected | Solid deposit, jets invisible | Overnight, then repeat | 4 hours, then repeat |
Materials that need care
- Chrome
- Tolerates vinegar well. Avoid abrasive pads, which scratch the plating permanently.
- Plastic / ABS
- Acid-safe, but keep the soak under 40 °C — hot water softens the moulding.
- Brushed / PVD finishes
- Dilute 1:1 and shorten the soak. Strong acid dulls the brushed grain.
- Rubber nozzles
- Hardening is the risk. Shorter soaks, more often.
- Gold / brass plate
- Use citric acid at half strength, and never leave it unattended for hours.
The bag method, step by step
- Fill a zip-top bag with enough vinegar to submerge the face — usually 300–500 ml. Check the seal by holding it upside down over the sink.
- Slip the bag over the head so the nozzles are fully under the liquid. Push it up until the liquid covers the faceplate, not just the rim.
- Secure it with a rubber band around the neck of the head. A second band at the top of the bag stops it sagging as it warms.
- Leave it. Overnight is the standard; four hours is the minimum for visible scale.
- Remove the bag carefully — it will be full of dissolved calcium and loose grit. Empty it into the sink, not onto the shower tray.
- Rinse and run. Flush for a full minute, then clear any remaining holes with a toothpick.
If the head is removable, soaking it face-down in a bowl works better than the bag: full submersion, no sagging, and you can see the progress. The bag exists for heads you cannot easily detach, or for renters who would rather not touch the fitting at all.
After the soak
Rinse thoroughly. Acid left in the nozzle cavities will attack the plating from the inside and will make the first shower smell like a chip shop. Run the shower hot for a minute, then cold, and check the spray pattern against a wall — even jets, no sideways spray.
Scale that survives an overnight vinegar soak is usually not scale. Check the inlet screen and the flow restrictor before soaking again — the restriction may be upstream, where acid cannot reach.
Keeping it clear
Descaling is a repair; prevention is cheaper. A monthly two-minute vinegar soak keeps the film from ever becoming crust, and rinsing the inlet screen at the same time catches sediment before it reaches the nozzles. The routine is in the prevention guide.
Written and reviewed by the Flow Restore editorial team. Community quotations are summarised and attributed to the thread they came from; they are not endorsements. Nothing here is a substitute for a licensed plumber's assessment.