What are safe uses of non-potable water?
While traveling, you come across many different levels of water safety. In some countries you can drink the tap water, and in others you should avoid it at all costs.
Where do you draw the line when you know the water isn't safe to drink?
- Brushing your teeth?
- Washing dishes?
- Washing your hands?
- Washing clothes?
Do you also have to avoid eating anything that's liquid unless it's hot?
I'll give an example. I'm staying at a guesthouse in Bali that has a shared kitchen. There's a sign specifically stating that the water is non-potable, but we are asked to wash our dishes there. So the same cups I would use for eating and drinking have been washed with water that isn't safe. I've been doing it for a week and have been fine.
I am assuming that your definition of non potable water is tap water, you can use tap water for anything ... as long as you dont drink it.
@user2704 - depends entirely on the country. Here in Scotland, tap water is likely to be better for you than many bottled waters!
This is hard to answer with an authoritative source since the quality of non-potable water varies widely from the source it comes from (is it groundwater? river water? is there anything recycled from drainwater from houses?) and even within a country.
I'm speaking mostly from my experience living in India, but in practice I have seen similar practices in Malaysia, Indonesia, Vietnam and Thailand too. None of these places have potable water supply; the source is typically river or lake water. The reason why they are classed non-potable is primarily because of high mineral content or particulate matter, which can be purified for human consumption by physical filtration as opposed to bacterial disinfection - although as it has become cheaper and more compact to make ultraviolet or reverse osmosis filters for home use, these are also used. Bacteria or viruses are the causes for most water-borne diseases, those can get into the water supply if untreated raw sewage is dumped into water sources which thankfully most civil authorities are not stupid enough to do.
So for the countries I mentioned, in practice, while it is customary to purify water for drinking either by boiling or using filtration devices, for other purposes such as washing clothes, washing dishes, cleaning hands, bathing, brushing teeth et al - essentially, anything that does not involve ingesting water, tap water is used directly. The water may taste funny for instance if you're brushing your teeth - that's because of the high mineral or iron content typically - but as for safety, yes, it can be considered safe.
A very rough bottom line could be indeed swallowing the water. Many sources also mention washing vegetables in a teated water. It is always under the assumption that the water is not contaminated, but only not-potable in one way or another.