We may be Overthinking this, but here Goes ...
There are grossly three scenarios:
-- Resident
-- Motor Vehicle
-- Backpack/Bicycle
If resident, then you can boil, distill, reverse osmosis, whatever you choose. Lots and lots of expats simply use a ceramic filter, boiling the candles or treating with chlorine once a month. In all of these cases, you are starting with city water which was probably safe when it left the plant, but has been contaminated due to low pressure, bad pipes, etc.
With a motor vehicle you are typically treating water in an enclosed tank. As always, you should take from the best source possible; city water, a soft drink plant or brewery, a hotel, a village pump from a deep well, etc. You want to avoid streams, bucket wells, pans, etc. Obviously, the dirtier the water, the greater the amount of pre filtering you want to do. You want to start with clear water if at all possible. I would then treat this water with chlorine, typically purchased as laundry bleach at a city or village store. You don't need much and you won't be storing it long. Finally, I would filter for taste and crud. The filter on my current truck claims to be good for cysts. Since I start with commercial camp site water in the States, I'm probably safe.
On foot, your options are more limited. I have used filter pumps and lots of folk swear by Steritabs or similar dry chlorine tablets. Iodine tablets typically taste so vile that people simply don't use them. There are also UV pens, but I have never used one.
The old "water in a bottle on the roof in the sun" actually works well, if you have the discipline to leave the water up there long enough. (And enough sunlight.)
Obviously, a lot depends on how long a trip and what sources you have available.