If you have specific "local knowledge" the spring, or the creek, has good drinking water, nevertheless look upstream for dead animals, sewage, or possible leaking septic tanks. I only drink from springs and streams I know, and I check each time I get water.
I have also had giardia. One and one half years later, I was rid of it. Even so, I could be a carrier. I do not share drinking or eating utensils, or containers. Giardia is bad. The drug treatment is bad. Be careful.
There are a number of reasonably convenient means of having good drinking water:
Carry water: I have Platypus brand plusBottle™ Holster 1-liter flat water carriers for drinking water. The carriers are insulated, to an extent. They have a comfortable shoulder strap I don't mind. The drinking water is at hand. I have two. Both start out, having fresh drinking water. Then, one becomes my water treatment receptacle. This is a minimum. If I am going out for more than one day and if I plan an overnight, of course, I have a larger Platypus Water Tank, for carrying water and for water for cooking.
Treat water: This video demonstrates Sawyer Gravity Water Filtration System.
I have a Sawyer in-line water filter for the gravity water filter system, because I can use it in towns on a thru-hike or near the trailhead, plus I can use it with my 1L or 2+L Platy Bottles or plusBottle with either the Platypus Quick-Disconnect Kit or Shutoff Valve accessories.
It should be noted, the Platypus GravityWorks/Cleanstream™ Filter Cartridge is available separately, either for replacement or to assemble your own gravity filter kit using the smaller 1L or 2+L Platy Bottles or plusBottle.
The 4 Liter Platypus GravityWorks™ Water Filter complete system is also available.
Sawyer has complete gravity filtration systems, shown at REI, that use their 3-way in-line water filter.
I "prefilter" with a cloth or one of the .4 micron prefilters available for widemouth water bottles, which I "dunk" below the surface using a hiking pole.
The inline water filter is suspended between the Platypus containers, for gravity feed. I do this during lunch break, or at the end of the day. I treat the water, inside the container by adding the right amount, and no more, of McNett AquaMira 2 part water treatment drops in plastic Microdrop dropper bottles. I wait for the amount of time for the water temperature. This is why I have two drinking water containers. One is ready for drinking, while the other is getting ready for drinking. I have the larger Platypus water container, full overnight, and ready for drinking and using the next morning.
The 4 Liter MSR Autoflow Microfilter has a top-opening water bag, much like the storage bags for kayaking. It is possible to rinse out this bag entirely.
I do not recommend iodine water treatments. No one should have iodine, very often.
I have seen hikers, using the Katadyn Exstream Purifier Bottle. If ultralight is for you, and if you do not mind a miniscule trace of iodine, I would use this product, by using a coffee filter or a cloth as an additional prefilter.
The Katadyn MyBottle Microfilter water bottle provides 0.3 micron filtration.
I do recommend water filtration, if the standard is 2 microns or less. However, I don't like to carry either the Katadyn Pocket or SweetWater Guardian water filters I have seen in use: they are heavier and bulkier than the system I prefer to use. If you always like to carry a rucksack, or a small pack, a water filter may be your choice.
My international adventure travel trekking friends insist the Katadyn Pocket water filter kept them healthy.
The SteriPEN has gained popularity, because it weights 4 oz. and 1 liter of water is ready in 90 seconds. However, the water must be clear. This means, cloudy water (silt, glacial runoff, or algae) will not be purified. Many people have a Steripen, for clear water, and have a backup system for everything else.
If you like a water bottle UV purifier, mÜV has a rechargeable battery.
My lightweight water filtration system is the in-line gravity water filter. My ultralight backpacking setup relies on the Katadyn Micropur MP1 Purification Tablets.
