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Hi John and Tim and also Graham Welland from Thames Water (who sent me some information directly).

Thanks so much for responding to my email which has been greatly appreciated and apologies for my silence to all of you. Have had a very busy few weeks working and travelling in country, including looking into this issue some more and wanted to have time to respond to your posts properly. Strangely I received John's email in my inbox and tried to send a quick reply of thanks by return of email at the time, but it seems this system does not work as my response was not posted. But for Tim's email I didn't even receive this in my inbox. I am new to Knowledge Point in this format, so not sure if I have the hang of it yet? I need to work that one out.

John thanks very much for the suggestion re cathodic protection and also other forms of waterproofing. We haven't discussed this option as of yet but I will add it into the discussion. I haven’t heard this mentioned but it would be interesting to know if it is a technique already available in country. In terms of the reason that painting is recommended as I understand it, it is for both preventing / slowing down the rusting process for steel tanks and also probably for a degree of waterproofing. I just found this interesting article which talk about various options including different types of epoxy paints in case you are interested: https://www.wwdmag.com/coatings/protecting-water-storage-tanks-era-environmental-compliance

Thanks very much Tim for your experience of using epoxy paints in Rwanda. That's also useful to know. I have also just established last week that in the country I am currently working in that epoxy based paints are produced in country (two part mixes) and used by one of the largest water tank manufacturing companies for the insides of water tanks; and also that a producer has also just started producing a bitumous paint. This particular company do their best to identify if the paint is safe for drinking water but there do not seem to be agreed procedures or processes for checking their safety for use in drinking water tanks in country at the moment. Painting inside tanks seems to be quite widely recommended as it is noted in various guidance and regulations, including for bottled water factories. I presume that at present most companies and smaller water tank users (such as water tanker or donkey cart operators) probably do not use such paints as they may not know they need to use a non-toxic paint and also using an epoxy paint apparently costs about 15 times as much as a standard paint off of the shelf so this is also quite a deterrent. Even when a system for certifying paints, sealants or other materials for use with drinking water is established (which seems to be quite complicated and will need sophisticated lab equipment and processes), there will still be significant challenges for enforcement and ensuring use; which I think would be similar challenges faced in many countries.

Graham also very kindly pointed me in the direction of the DWI website (https://www.dwi.gov.uk/drinking-water-products/index.htm) and their list and procedures for applying for approval testing for paints and also provided a further contact for more details, which is also really helpful and I will probably take up at some point. Both epoxy resin and polyurethane based paints are included on the DWI approved list of site applied coatings for water retaining structures for inert tank materials such as metals and cement based structures (pp48-50).

Thanks so much again for taking the time to respond to my question. It has been much appreciated and I will be sharing the various suggestions when back in country.

Many thanks.

Sarah