CELEBRATE WHEN IT RAINS
If you live in an area that receives pretty decent annual rainfall, collecting and using rain water domestically is totally feasible. The bigger the roof you have the more you get, it that simple, but even with a smaller roof, with adequate rainfall you can really fill 'em up. Again, with all off grid ventures conservation is critical, but that doesn't mean running around outside with no shoes and a dirty face and smelly armpits (unless you want to of course!)
DIVERT YOUR GUTTERS
I have mine running into a 4 in pipe I have buried in the ground that runs into and underground cistern. But before it goes into the cistern, it gets filtered by this really awesome stainless steel screen that stops anything over 200 microns from getting into the tank. It can also be quickly removed and cleaned when needed.
TREAT YOUR WATER
I pump water from my holding tank below ground to another tank of smaller capacity. I then treat it with bleach, a very small amount. There are also more complicated ways and expensive techniques such as using ozone for example if you did not want to use chemicals.
I then pump it through sediment and carbon filters to make it super clean and absorb any chemicals picked up from the roof and collection plumbing as well as any bleach that was used to sanitize the water in the treatment tank.
CAN YOU DRINK RAINWATER
At this stage the water is completely fine for most domestic use like showering and washing dishes for example. Can you drink it? Maybe so. Taking another step in the filtration process to the sub micron level will guarantee safe drinking. Because I have a pressurized system I use a ceramic inline filter under my sink with it's own dedicated faucet in the counter top.
We have been drinking rainwater for many years using these techniques and practices successfully. Another nice feature and benefit is the increased lathering of soap when you shower due to the PH. Ultrafiltration makes the best tasting water too!