Live chat with water scientists Mark Smith and Adrian Clark


Welcome all, it is a pleasure to have hosted the second live chat organised by The Nappy Science Gang! Below you will find the write-up of what has been discussed over the course of the hour with our two water experts, Mark Smith and Adrian Clark, both members of the Royal Society of Chemistry Water Science Forum.

Mark Smith worked as a Laboratory of the Government chemist before becoming water quality manager and then moving to the Drinking Water Inspectorate where he was Research and Contracts manager as well as an Inspector. He finished up being the Research Program manager for the then Department of the Environment, Transport and the Regions Water and Contaminated Land Research program. Adrian Clark worked as a Senior Professional Scientist and Project Manager prior to his retirement. He is a chemist by qualification and has worked on a wide variety of projects including ones related to water science.

I hope you will both enjoy and find this read useful!

Q: For a non science person, please can you explain what ‘surfactants’ are?
Adrian: They are essentially the same as detergents as used in washing up liquid. They improve wetting of fabrics and aid in lifting dirt along with mechanical action (in the case of washing machines). I should also say there are a host of other ingredients such as enzymes in biological detergents, water softening agents, etc.
Mark: I think we need to get back to basics. Water on its own will act as a solvent and will remove dirt or soil. If you apply mechanical action with water, this will remove move dirt.
Adrian: So will beating clothes on a stone in the river!
Mark: But if you add a surfactant it will remove more dirt.
Adrian: Remember you want to have some clothes left afterwards, so the gentler the action the better, hence detergents will help!
@Mark and Adrian, I guess as a group we’re interested in removing a specific kind of ‘dirt’ – to put it bluntly, removing poo from nappies. So water alone would remove this, but there are questions of hygiene vs. damage to nappies
Mark: Water alone would eventually remove all dirt, but it would take a long time, and you would need to keep changing the water.
Adrian: Pre-soaking is a well known way way of loosening dirt before washing.

Q: This leads me to my next question. Most cloth nappy users these days don’t soak their used nappies in a bucket, so we rely on what happens in the washing machine to both remove dirt and kill bugs. We’re particularly interested in the best washing cycle to do this.
Adrian: How long might soiled nappies be left to stand (ie incubate their contents)?
@Adrian, in our latest chat Penny Broderick was saying that people typically leave them around three days, but some might leave them up to seven days.
Adrian: This will place more emphasis on a thorough wash cycle and may result in growth of bacteria. I think 24 hours is about the maximum I would want to consider. What do you say Mark?
Mark: I am afraid it depends upon the particular machine you have. Machines are designed to be economical with respects to the amount of water, detergent, temperature of wash and mechanical action.
@Mark, that’s really interesting as it raises questions about how eco-friendly and money saving cloth nappies are. If I washed every day that would only be about 2-3 nappies which doesn’t sound very eco-friendly!
Mark: The majority of clothes that are washed nowadays have a low soil load and only need refreshing and not much stain removal. Both the manufacturers and consumers want eco-friendly machines with low water usage and quick washes.
Adrian: It seems a shame that nappy manufacturers are not more attuned to offering advice on how best to clean their products and ensure good hygiene. This need not involve specifying brands of detergent. Likewise machine manufacturers should think about cycles for their particular machines.
@Adrian, manufacturers do offer advice, but the advice from different companies is often conflicting. Then also each ‘Mum on the Street’ has a different opinion. I think most of us would like an independent expert opinion.
@Adrian, yes the advice varies hugely and there are so many urban myths like “liquid detergents coat your nappies” that get repeated over and over until people believe it must be true. Some independent expert advice is what we need!

Q: Do you have any opinions on which temperature would be best for removing thrush and/or other bacteria (e.g. E.Coli)?
Adrian: Advice used to be to boil whites (my wife still does). A temperature of 60degC will deal with most bacteria within a few minutes. Sunlight will also help sterilise garments.
@Adrian, but there is also the additional issue that some nappies can’t or aren’t labelled as safe to be washed above 40degC, in which case you are relying on detergents to do most of the bacteria removal. We have had some discussion about using sunlight to kill bacteria (and bleach stains). Interestingly, the labels on my bamboo nappies say to avoid too much exposure to UV.
Adrian: I would be wary of fitting the wash to suit the fabric rather than the other way round unless manufacturers can provide good evidence for their recommended wash.
@All, for me, bamboo or not – it goes in at 60degC.
@All, I also wash all my nappies at 60degC regardless of the manufacturer advice.
@All, me too!
Adrian: Good to hear some of you have experimented with using higher temperatures and are happy to follow your own intuition. Maybe some of this information can be passed on to others who might not be happy with their own washing.

Q: So what are your recommendations to wash cloth nappies?
Mark: It is difficult to give exact recommendations because with nappies the soil load is higher than most comparative tests that are undertaken and the material load is not normally tested on its own.
@Mark, What do you mean the material load is not normally tested on its own?
Mark: In general when you test stain removal, you impregnate a cotton material with a stain producing substance. You let it set for a period of time. You then subject that sample to a washing cycle. But you include a base load of material to ensure you get the correct , normal washing characteristics
@Mark, so the material load is the extra stuff put in to bulk out a load and make it more like the normal experience of being washed?
Mark: It is what you would expect in a “normal load”. Remember the machine is designed for a minimum and maximum load. If below the minimum load you will not have an effective washing cycle.
@Mark, to clarify – is the lack of effectiveness at less than the minimum load because there won’t be enough mechanical action (as in fabric rubbing together) to wash properly?
Mark: It depends on the machine, you have mechanical action, you also have in sensor machines less weight meaning less water which will affect efficiency.
@Mark, common advice on nappy forums is to add a towel or two to the load if you have a small load – to bash everything around more and to fool the machine into adding more water. Would you say that is good advice?
Mark: Yes you need to get the weight up, a ballast load for stain removal testing does include blankets or towels.

Q: Do either of you have an opinion on Bio vs. Non Bio & Liquid vs. Powder?
Mark: When you do stain removal testing it is normally done on cotton cloth, this is because the microscopic fibres on cotton are harder to remove stains from than synthetic fibres. If we look in a formulation strategy for stain removal, in general powders are better than liquids, white products are better than coloured products, biological are better than non biological.
@Mark, So, polyester and things like microfibre will have stains removed more easily than cotton? That’s interesting. How do the other materials commonly found in nappies compare? (i.e. hemp, bamboo and zorb)
Mark: If you look at electron microscopy of the fibre structure in general cotton has a higher surface area and is more irregular leading to more soil being trapped.
Adrian: Hemp fibres are hollow, I am not sure about bamboo, but these fabrics are presumably chosen for their capacity to absorb liquid and offer a large surface area. They may behave in a similar way to cotton in terms of retaining different stains but I cannot be sure. It is also important to use the correct quantity of detergent for the degree of soiling, especially if bleaching activity is to be retained. This will get “used up” in contact with organic matter (poo) unless sufficient surplus is present.
@Mark and Adrian, interesting – the worst staining nappies in my collection is Bumgenius elemental which has an organic cotton absorbent part (similar to soft t-shirt material).
@Mark and Adrian, Yes, I’ve always found that my nappies with natural fibres stain much more easily than those with a fleece/polyester lining.

Q: Is ‘detergent build up’ an actual problem?
Mark: Most people overdose detergent. There will always be some retention within a material. Some washing products have an enhanced efficiency due to enzyme absorption over multiple wash cycles.
@Mark In cloth nappy circles, I think the opposite is probably true! Lots of people only use a tiny amount of detergent because they’re worried about ‘build up’ and then they wonder why their nappies aren’t clean!
Adrian: I would be wary of suggesting overdose, the issue is having sufficient active ingredient. I agree there may be other components which may be left behind with insufficient rinsing. There could also be an issue with residues left in the machine.
@Mark, does that mean that some products work better if you use them regularly?
Mark: Some products are formulated so that if used regularly they provided a modification of the fibre surface that aids stain removal.
@Mark, Does this mean that they coat the fibres with something and make them smoother?
Mark: that is correct.
@Mark, the thing the fibres are now coated in, does it affect the absorbency of the fabric? Because obviously for most clothes you aren’t bothered about the absorbency, but for nappies you are.

Q: Could you explain how having hard or soft water would make a difference to washing heavily soiled laundry? I think a lot of us get the gist of it, but it would be nice to have expert opinion to back that up.
Mark: The different between hard and soft water in terms of detergent efficiency is the harder the water, the more detergent is lost in dealing with the hardness of the water. Manufactures deal with this in their product dose recommendations. If you have a plumbed-in water softener it works by exchanging Ca and Mg ions with Na ions. You must by law have a separate unsoftened water supply for drinking and cooking as the Na content can be harmful. Water companies and some industries bulk soften using lime which does not have the increased Na levels, but it is not applicable due to scale constraints for domestic use.

Q: My nappies say don’t use any water softener products like Calgon, but my water is so hard that I worry about my machine if I don’t. Also, in hard water detergent manufacturers recommend using more detergent. Do you have any suggestions about hard water areas? Softener/more detergent?
Mark: Calgon will result in smaller crystals for harness salts. This prevents build up and prolongs life. In terms of washing efficiency it has no effect on effectiveness. With synthetic detergents you do not need to increase dose as much as with soap based products, but you should follow manufacturers recommendations as they have tested their formulations in different water types.

Q: So now I am just left wondering what the mysterious pink stain actually is…
Adrian: There are probably various recent changes in practice which have led to a resurgence of the pink stain which has previously been termed “red nappy syndrome”. This is due to bacteria (although there are also other possible causes) and leaving buckets containing soiled nappies to fester at room temperature is the most likely contributing factor.

At the end of the chat, Sophia, coordinator of the Nappy Science Gang, announced the three questions that were voted by the NSG community over the course of the previous weeks as “main scientific questions to investigate”. And these are:

1. What’s the best thing to wash with (Bio/non-bio liquid/powder/ec o eggs/soapnuts)?
2. Is ‘strip-washing’ cloth nappies necessary? If so, what is the best method?
3. What is the optimum temperature at which to wash cloth nappies and why?

Tonight’s chat has been fantastic – so much to think about for the group. Thank you all for coming and asking such great questions, and Adrian and Mark thanks again for your time and your detailed and incredibly interesting answers.

7 thoughts on “Live chat with water scientists Mark Smith and Adrian Clark

  1. Have you thought that possibly that the pink stain could be produced by Serratia marcerscens? It is an enterobacteria commonly found in the guts of children, produces a pink / pink-orange stain. Found in bathrooms usually, thrives on damp.


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