Do you know how to make water from open streams safe to drink? I know that ground water is not safe but in an emergency situation would it be possible to make it drinkable?
First, gross filtration- get the twigs, dirt and other organic and nonorganic junk out of it. Then run it through a straining filter, which can be several feet of sand in a piece of PVC plastic water pipe, a Berkey or other ceramic filter, or anything of the like. At this point, most of the microbiological material should be removed and you can move onto the final stage. Boiling works. So does exposure to sunlight[SODIS], or chemical treatment with bleach or HtH, as described above.
That's probablt as good as you'll need, and likely the best you can do under field expedient conditions. It probably won't do in the event of serious industrial or military contamination of the water supply with toxins or heavy metals, but unless you can test for the presence of such hard-core contaminants, there's little else you can do anyway. Do the best you can, and pick a *designated drinker* to go first as the guinea pig for your family or group.
More: read this, then watch this.
Berkefeld water filters are my favorite and they will purify pond water, puddle water, etc. They now have fancier ones than when I bought mine, that will get out most pesticides and other chemicals that the regular ones may not.
They have a variety of sizes, too. An outfit called Pleasant Hill Grains has the best prices I’ve seen and good customer service (last I got anything from them). I don’t have a link but you can easily find it with a search.
Iodine Tablets are what the Army sometimes uses.