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If forced to use a rule of thumb when splitting water requirements along the lines of potable water and water for washing, flushing etc in emergencies then I'd aim to supply 3 litres per person per day of potable water for drinking and try to achieve that. As Harriette has pointed out the sedentary minimums may be less but the actual amount needed will depend on climate, level of activity and exposure to heat/sun/extent that people sweat and how much water comes from food. In other words the 3 litres pppd figure is a safe figure for 'public information consumption' to aim for. Averaging in this way is probably ok in that smaller humans drink less water than bigger ones.
UNHCR guidance states that a minimum of between 3 and 10 lpppd is required but should rise as soon as possible to 15 lpppd. In other places the minimum is stated as 7 lpppd.
I have seen a table of how water usage splits but cannot think exactly where to find it and it is bound to be only appropriate to a certain context (I think I saw it in the S Pacific in relation to the recent drought in the Marshall Islands)
This may be useful: https://www.spherehandbook.org/en/water-supply-standard-1-access-and-water-quantity/ and alternatively presented in a cute way: https://www.ineesite.org/eietrainingmodule/standards/watersupply/accessAndWaterQuantity.php
One way to focus your internet searches is to append filetype:pdf to searches making documents come to the fore.
Hope the above helps.