Many folks around here have pools, which is the ultimate usable water storage method. You can't just drink pool water, though. You have to have a method of making the water potable. Boiling, distilling, water treatment tablets and filtering are all effective, depending on what chemicals the pool has been treated with in the first place. If I didn't know what chemicals were used, I would distill. Our pool is a salt water pool and we add very few other chemicals, so I would be comfortable just boiling and/or filtering the water depending on the use.
I recommend keeping some test strips on hand to check your water sources. Knowing what's in your water can help you know how to treat it the most effectively.
We have had a Berkey water filter for years. I highly recommend these. They can make the worst water potable and safe. We have the largest one and am I ever glad I bought big! We still have to fill it at least once a day. This is something that I think every single family should have.
We keep a Sawyer water filter or a LifeStraw in each of our bags, for use on trails, when hiking or for filtering water from less than ideal situations. Lifestraw also makes a filtering cup that is good for filling up at gas stations/spouts/spigots where the quality of the water is unknown. It makes me much more confident when drinking from sources I don't usually drink from.
A SteriPen is another handy tool for quick cleaning water. We have one and have used it on spring water when we were hiking. Didn't get sick, so that's good!
Keeping clean water on hand for immediate use is a wise step. There are lots of ways to do this. Buying cases of bottled water is the easiest way to start. They stack well and are cheap at big stores like Costco. You can get gallon sized water bottles at most grocery stores, too. They are harder to store.
Some people like to use water bricks. They are an investment, and must be stored properly, but can help you store a good amount of water in a small space. I don't have any of these.
A WaterBob or AquaPod is a must for quick emergency water storage. When an event happens nearby, you can quickly fill the bag before water pressure drops and the pumps stop working. You then have lots of water, conveniently stored and easy to use. I would choose AquaPod over WaterBob because it is made in the USA and the quality seems better, but either would be a welcome item in an emergency.