Always make sure your water is drinkable. You don't want to take any risk. See how to purify it for more information.
Water is by far one of the most important ressource you need to have constant access to. Furthermore, it needs to be drinkable.
In our modern societies it's a common good that we can find everywhere very easily. However it should never be taken for granted.
Indeed, the public water can be affected by bacterial contamination, issue on the network, serious drought causing water restrictions, too much fluorid, ...
# Where to find it?
If you have a place to live in, then it's as easy as opening the tap.
Otherwise the common spaces to find some is in cemeteries, public building like libraries, fountains or public toilets.
You can also ask any cafe/restaurant and they should provide you with a glass of water.
You can collect some if you find a source or a river.
You can also get some from the sky, for free. Yes, never forget the value of rain!
# How to collect it?
If you are 100% sure it's drinkable water then just open your hands and drink from it. You can also bring your empty bottles / jerricans.
If you have a roof you can easily collect the rain water through gutters and then fill up a tank. Obviously you can design way more advanced systems of water collection with filtering, water pump, overflow management and so on. Feel free to search for it.
It's also possible to use a simple tarpaulin that you attach to trees to collect rain water into a bucket.
# How to purify it?
The simplest, cheapest and oldest way to do it is to bring your water to a boil. If the water is boiling you're sure that you killed all the pathogens.
Boiling will NOT remove chemical toxins like pesticides and so on. So be sure of where you are taking your water from. Also it's recommended to filter your dirty water through a piece of clothes to remove the sediments. A coffee filter is a good solution for this task.
You can buy (or create) a water filter system. You can find some working with gravity where you pour your water in the top compartment and it will slowly fall down to the compartment underneath passing through filter (usually active coal & sand).
If you have the budget a life straw is also a good solution. It allows you to drink safely from any water.
Never forget that filter system and life straw both have a limited timespan after which there are not affective anymore.