An article in the Daily Mail last week related an individual's experience with a device sold to conveniently provide water at the correct temperature to make up into babymilk. Warmed water will support the growth of some microbes and algae so the device has cleaning cycles which have to be run regularly according to manufacturers instructions. This is intended to eliminate microbial growth.
Several parents have apparently been complaining about this device making their children ill and one decided to take their machine apart to search for any obvious apparent causes of ill health. It rapidly became clear that the tubing that carried the water tended to darken with a film developing on inside surfaces. More strikingly there are images of an inline filter that has accumulated a dark substance that they are assuming is a mould and are linking the presence of this substance to coughs and colds in their children.
Unfortunately there has been no apparent attempt to properly identify the dark coloured deposits so not surprisingly the manufacturers are suggesting that it might be carbon deposits or other chemical residue. I would suggest it might be mould or an algae if light can get into the machine, particularly in the parts that store cold water. A hot water flush would tend to kill off algae but some fungi are quite resistant - which might be present depends on where in the machine these deposits came from.
Greater clarity is needed here to establish whether or not there is an issue with these machines with regard to encouraging microbial or algal growth in contact with drinking water intended for babies. If these machines are not clean then they certainly could be a risk to health. Perhaps an independant specialist laboratory for the testing of this equipment would be best - there are several Mycology Reference Centres for the detection of fungi around the UK e.g. in Bristol, Cardiff, Leeds & Manchester run by the UK Clinical Mycology Network https://www.gov.uk/government/groups/uk-clinical-mycology-network