Suitable roof paint for water collection for domestic consumption

[Ropetangler]

G'Day Folks,
I would appreciate some advice for paint suitable for a small section of roof over my wood shed, which is part of the rain collection used for domestic supply. The roof in question is only small, 2.4M x 4.2M, so a little over 10 sq metres in area. The closest specialist paint supplier to me is part of the Inspirations paint franchise, and I have always found them very good to deal with, but unfortunately on this occasion the only suitable paint that they had was only available in 10 Litre drums worth north of $200. They advised that as far as they knew only Wattyl had a suitable paint in smaller quantities but no one as far as he knew stocked it locally, although a hardware store 18Km away might have it. As it is a long weekend here, I phoned to see if they were open and if they had it and was assured that they had paint suitable for rainwater collection surfaces, so went over and collected it. The paint that they said all the local professional painters use for roofing was Haymes exterior Solar Shield, and again I discussed with the sales assistant the need for safe drinking water from the roof, and she did suggest that I divert the water for the first rain after the roof is painted, but after that it should be good for collection. The instructions on the 2 L paint tin were difficult to read, being small print in black on a darkish gold/brown background, but upon reading it all when I got home and had the tin in good light, I was surprised to learn that Haymes do not recommend this paint at all for roofing or contact surfaces.
I have not mentioned that I am painting this skillion roof because it has rusted severely. This is most likely because water from the main building which has a Colourbond and Zincalume roof runs over the galvanised skillion. I am aware that mixing galv with zincalume leads to rusting issues, but it has lasted 35 years so far, with no paint protection, so I am hoping that with some TLC now it may last another 20 years or so and then it will most likely be someone else's problem.
I have removed the iron at the moment and replaced some woodwork, a rafter and a purlin, the rest of the roofing timbers look pretty sound, although some has been affected by water leaking through over the years, so while the iron is off I plan to paint the wooden rafters and purlins, and I have already water blasted the iron and electric wire brushed the loose rust and applied Ranex rust converter. I want to paint it now on both sides and patch several pinhole rust penetrations with Sika polyurethane, then get it back up and fastened properly with roofing screws, (it was mainly fastened with clouts previously, most of which had come out, allowing water ingress), and then a final topcoat with the suitable roofing paint.
As a matter of interest, this galvanised iron profile resembles that used in domestic roller doors, it is not a profile usually used for roofing. There is a bit of this stuff around the place here, the original builder was a senior staff member at a large local plumbing concern, and the sheets are 1220 X 2400, and I suspect that they may have been some kind of cover sheet around rolls of colour bond iron sent out by Lysaghts to companies forming their own sheet metal profiles.
If you have waded this far, thank you very much, probably way too much waffle, but what I need is:

1.suitable non toxic paint.
2. available in 2L preferably quantities.
3.Colour is fairly flexible, I bought white gloss today, building is presently mostly faded brown Colourbond somewhat lighter than the present Colourbond Jasper, but there has been a small addition which just has a Zincalume roof and we have the galvo section I am discussing here. It is just a wood shed and we are out in the bush in NW Tasmania.
Thanks in advance for any insights,
Rob.

[verawood]

G'day Ropetangler

A bit of a start

https://www.tremco.com.au/fileshare/...ta%20Sheet.pdf

prob find similar products

[Beardy]

Rather than looking in the paint section have a look at paintable membranes in the waterproofing section, they will work fine if you choose a trafficable UV stable product. Bunnings has a number of them

[riverbuilder]

If the sheets are off, why not just replace them?, new sheets are only going to be around$190. Job done.

[Ropetangler]

Thanks to all who have replied to this thread, strangely I had been wondering about the cost of replacing the roof entirely, but had not made any enquiries regarding cost when Riverbuilder made his suggestion. While the job is not yet completely finished, there is a new roof over my firewood with rain forecast for the next few days. I still need to trim back some overhanging rafters on the main structure, to increase the clearance from the new zincalume on the skillion, because the corrugated profile is about twice the thickness of the old roof which had a profile only about 10mm high, and presently while all sheets are in, 2 of them are jammed in under the overhanging rafters, but as I was running out of daylight, I just put a single screw in each loosely at the far end to hold them till I fix the clearance issue. The other sheets only have 4 screws in each holding them so I have to complete the fastening, and fit some flashings, + plumb in the gutter to the downpipe and then the job will be done.
Thanks to to Verawood and Beardy also, I am not familiar with either of those product types, and I will inform myself about them for any future use, either for my own benefit or the Community Shed where I spend plenty of time. I do vaguely recall my late father using something similar to the Tremco Hydraseal product, I think it may have been made by a mob called Pabco, but it was a much thicker consistency as I recall, perhaps for sealing bigger holes in roofs or guttering, and definitely not spreadable with a stiff brush, or even a trowel on a large surface. Cheers All,
Rob