Windscreen Washer Fluid: Why Concentration Matters in Winter
It's a small thing that a surprising number of drivers get wrong every winter, topping up with plain water because it's free and available, without realising what that actually risks in cold weather.
Why plain water is a problem in winter
Water freezes at 0°C. Proper screenwash concentrate contains a mix that lowers the freezing point significantly, often down to minus 15 to minus 35°C depending on the concentration used. Plain water in the washer bottle and lines can freeze solid on a cold night, and expanding ice inside the lines or pump can crack them, turning a free top-up into a repair bill.
Getting the concentration right
Screenwash concentrate is diluted with water, and the ratio matters more in winter than summer. A stronger mix, sometimes used undiluted or close to it in genuinely cold conditions, protects against freezing more effectively than a weak summer-strength dilution. The bottle's own instructions usually give a seasonal guide.
What happens if it freezes anyway
Beyond the immediate inconvenience of no washer fluid when you need to clear road grime, a frozen and then thawed system can develop leaks at joints and seals that weren't a problem before, since the ice expansion can crack components that then leak once everything thaws.
A cheap habit worth keeping
Keeping the reservoir topped up with a properly winter-strength mix costs very little and avoids both the frozen-solid scenario and the more expensive repair that can follow it.
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