Dosing detergent by water hardness

Short answer: Short answer: the package states three doses for soft, medium and hard water. Look up your municipality's water hardness and use the right one, not the middle one, otherwise you dose either too much or too little for the water actually coming out of your tap.

Why hardness matters

Limescale in the water binds to the detergent, so part of it gets used on the water instead of on the dirt. With hard water, more is needed to get the same effect. With soft water, the middle dose is too much, and the excess ends up as residue in the fabric.

How to find the number

The water utility or municipality states the hardness on their website, often under a page about drinking water or water quality. It is given in degrees dH, and the package translates that into soft, medium or hard. Write the number down and use it every time, instead of guessing from wash to wash.

Adjust for load size and dirt too

A half full machine needs less detergent than a full one, and lightly soiled laundry needs less than heavily soiled laundry. The dose on the package applies to a full machine with normally soiled laundry. Check out bamboo clothing for women for examples that typically only need a light dose.

What happens with too much detergent

Soap residue stays in the fabric, laundry becomes stiff and grey over time, and odor settles into the fibers more easily after each wash. It can also irritate the skin of sensitive people, since detergent residue sits directly against the body all day once the clothing is worn.

What happens with too little detergent

Dirt does not get bound and settles back into the fabric as a greyish film, especially visible on light colored laundry. Over several washes that can leave a persistently dull feel in the clothing, even though it has just come out of the machine and technically been washed.

Liquid, powder or capsules

Liquid detergent is gentle on fibers and dissolves reliably at any temperature, while powder often works better against stains and limescale at higher temperatures. Capsules dose automatically correctly but give you no way to adjust for hardness, load size or dirt level yourself. Check out bamboo underwear for women for laundry that does fine with gentle liquid detergent.

Does the UK have hard water

It varies a lot between regions, from soft water in some places to very hard water elsewhere in the country. Look it up rather than guessing, since the difference between regions can be large enough to change the right dose noticeably from one address to the next.

How to adjust for the season

Sweat and skin oil increase the amount of dirt that needs binding in summer, so a bit more detergent can make sense during warm periods. In winter, when clothing is often thicker but less soiled by sweat, you can comfortably stick to the normal dose without issues. Check out bamboo towels, which are often washed with a higher dose.

How to test your own dose

Wash once with the recommended dose and check the laundry once it is dry. If it feels stiff or looks grey, that signals either too much or too little detergent. Adjust slightly and repeat the test until the result feels clean and soft with no residue.

Frequently asked questions

What happens with too much

Soap residue stays in the fabric, laundry becomes stiff and grey, and odor settles in more easily. It can also cause skin irritation for sensitive skin when residue sits against the body.

What happens with too little

Dirt does not get bound and settles back into the fabric as a greyish film, especially visible on light colored laundry after several washes without adjustment.