Connecting a washing machine to a softened water supply
Connecting a washing machine to a chemically softened water supply can cause problems with detergent performance. Very soft water prevents detergent from dissolving properly, which can leave residue on laundry and cause excessive foaming. Some manufacturers specifically advise against using a fully softened supply. Electronic water conditioners fitted to pipes are a different matter and are not subject to the same concerns.
There are two quite different types of water softening system commonly used in domestic properties, and the advice about washing machine connections differs significantly between them.
Two Types of Water Softening – and Why the Difference Matters
A full water softening system using ion exchange resin to physically remove hardness minerals (calcium and magnesium) from the water supply. This produces genuinely soft water – often very soft water. This is the type that some manufacturers advise against connecting a washing machine to. More common in countries with very hard water supplies, but present in some UK properties.
Devices clamped to the outside of a pipe that claim to reduce limescale formation through electromagnetic treatment. These do not chemically soften the water – the mineral content remains the same. They are not subject to the same concerns as full chemical softeners. Their effectiveness is also frequently disputed.
The guidance below applies specifically to full chemical water softeners, not to electronic conditioners.
The Problem With Chemically Softened Water
Modern washing machine detergents are formulated to work with water in a range of hardness levels. Very soft water – as produced by a full chemical softening system – falls outside this range in a way that affects how detergent behaves.
Detergent does not dissolve correctly
In very soft water, detergent – particularly powder detergent – can fail to dissolve fully during the wash cycle. This leaves detergent residue on laundry. The effect is most noticeable as white streaks or powdery deposits on dark fabrics. Using an extra rinse cycle helps but may not completely resolve the issue. See our guide on too much foam in the washing machine for related detail on detergent and water softness.
Excess foaming
Soft water produces significantly more suds from the same quantity of detergent than hard water. If the detergent dosage is not reduced to compensate for the soft supply, excess foaming can result – which itself affects wash quality and can in severe cases prevent the pump from draining correctly.
The detergent dosage dilemma
Reducing the detergent dose to control foaming risks underdosing for the soil level of the laundry – resulting in poorer cleaning performance. The balance point between enough detergent to clean effectively and not so much that foaming becomes a problem is narrower with a very soft supply than with harder water.
This guidance also applies to households in naturally very soft water areas – parts of Scotland, Wales, and the south-west of England – even without any water softening equipment fitted. The same detergent dosage adjustments may be needed. Check your water hardness with your local water company if unsure.
What to Do If Your Washing Machine Is on a Softened Supply
- Reduce the detergent dose to the minimum recommended quantity for your load size and soil level – the soft water dose rather than the hard water dose shown on the packet
- Use the extra rinse option if your machine has one – this helps flush residual detergent from the laundry more thoroughly
- Check the instruction manual for your specific machine – some manufacturers include guidance on softened water connections and may specify connecting to an unsoftened supply or a bypass tap
- Consider whether a bypass connection – feeding the machine from an unsoftened tap rather than the softened supply – would resolve the issue if problems persist
Related Guides
Is Calgon Worth Using?
Whether anti-limescale products genuinely protect your machine – and how they interact with detergent dosage.
Limescale in Washing Machines
How limescale builds up in hard water areas, the damage it causes, and how to prevent it.
Too Much Foam in the Washing Machine
Why soft water causes excess suds and how detergent dosage affects foam production.
Hoses and Plumbing Compatibility
Whether new machines use the same hoses and plumbing connections as older ones.
Frequently Asked Questions
Can I connect a washing machine to a softened water supply?
It depends on the type of softening. A full chemical (ion exchange) water softener produces very soft water that some manufacturers advise against using as the sole supply to a washing machine. The water can cause detergent to perform poorly, leaving residue on laundry and causing excess foaming. An electronic water conditioner clamped to the pipe is a different matter and does not produce chemically soft water.
Will a softened water supply damage my washing machine?
A chemically softened supply is unlikely to damage the machine itself. The problem is with wash results – detergent performance is affected, which leads to residue on laundry and excess suds. Adjusting the detergent dose to the soft water quantity and using an extra rinse can mitigate the issue.
My machine is connected to a softened supply and I am getting white marks on laundry – what should I do?
White marks or powdery deposits on laundry from a softened water connection are usually caused by undissolved detergent residue. Reduce the detergent dose to the minimum recommended quantity for soft water and add an extra rinse cycle. If the problem persists, consider connecting the washing machine to a bypass tap that supplies unsoftened water, or contact the machine manufacturer for guidance specific to your model.
Hello S. I have a separate article linked to at the end of this article, which you should read. Essentially if you use the right amount of detergent and ensure that is good quality detergent then you should not need any other water softener. It might not hurt to use Calgon. If you do use Calgon you are supposed to reduce the amount of normal detergent to the dose for soft water. As far as I can see it’s the main function of Calgon because essentially it is only doing what the detergent already does. So the main point of using Calgon as far as I’ve been able to work out, is so that you can use less detergent. I’m unsure if the combination of limescale tablets and less detergent would be cheaper or more expensive than using the highest dose of detergent for hard water or not. Probably not is my guess but I don’t know if anyone’s ever worked out the maths.
Here is the article, Is Calgon Worth Using?
Just had new machine & dishwasher put in but the kitchen fitter didn’t connect them through the new Softner seen limescale build up in dishwasher already so do I use Calgon or get it connected to Softner? Don’t want my machines ruined as really hard water here in herts! Our last water Softner was used with machines & no limescale problem?
Thanks Kathi. And thanks also to Alex’s comment from a few years back. It looks like I might have missed it before.
Alex- thanks for the chemistry input. I have that precise type of ion exchange- which removes pretty much all minerals (because I need to remove iron). The problem is ever since the filter, the clothes are getting ruined. I have since turned off the polyphosphate additive, knowing this is a ‘sequesterer’ of what, i’m not sure, but the purpose is to deposit scale on pipes to avoid corrosion.
My laundry is better, fewer tears, but things are stretched and weak. I have now just started adding magnesium sulfate and by gosh I see a difference. They come out less crunched (wrinkled absurdly) and feel a tad bit sturdier. I want to also try calcite- so basically I am trying to turn the water into what it was before, less the iron.
I am also assuming the calcite (gypsum) will absorb some of those excess salts, which may be softening my fabrics too much. Do you think this last one will be a mistake? (calcite) I don’t want calcium deposits or anything that will damage the washing machine. I just want balanced water.
I finally did find some research stating that these precise minerals are used in the industry to give body and stability to fabrics. Just what they need to endure the spin cycle.
I have yet to try re-shrinking those stretched out lifeless clothes with hot water and a hair dryer / or pellet stove. I’m afraid IT will stress the fibers. Will have to test. As it is my sleeves are well over my hands and sweaters are limp and baggie, PEOPLE ARE OUT OF THEIR MINDS TO WANT SOFT CLOTHES- SOFT WATER !!!!!!!
(thanks to whitegoodshelp for these helpful articles/comments)
Hello Rob, it could be detergent residue as detergent doesn’t dissolve easily in very soft water. Make sure you reduce the amount of detergent used to that recommended for soft water. You could also try selecting extra rinse option if available or making sure you don’t use eco wash cycles that might use less water and make rinsing less effective. As a last resort you could try doing a few extra rinses.