Water from rivers and lakes

I would recommend chemical treatment, assuming the water source isn't cloudy or has a lot of suspended particles.  Those issues could be handled by a simple pre-filter that doesn't do any purification.  Iodine has taste issues.  Aqua Mira would be prohibitive from a cost standpoint.  In this case I recommend plain bleach added while the tank is being filled so it mixes.  6 teaspoons for 30 gallons.  Let it sit at least an hour, more if it is cold water, and you'll be good.  You may want to go even longer to ensure it handles the nasties like Giardia.  There will be a slight odor and taste but it will be a much easier and faster procedure than mechanical filtering.