Are there any long term ways to filter rainwater?

I know you can make water filters using different natural materials but do they last long? My main source of water will be from rain or nearby springs and I want to be able to make a water filter that lasts for a while but still filters the water good.

That old standby, the sand filter, is probably the simplest. The reason is that is replicates what goes on in nature:when rain hits the ground, it picks up bacteria, algal spores, and all sorts of other little critters. But as it seeps into the ground and percolates down, everything that needs oxygen to survive tries to move up, into the zone where there is pore space between the soil particles and they can breathe. Once water seeps down through a clay lens into more sand, suddenly the pore space is all filled with water and there is no air to breathe. In hydrologist speak, you've gone from the vadose zone to the phreatic zone. This is the zone where you find clean well water.

You might even be able to do nature one better by having a layer of activated charcoal on top of the sand layer. With the charcoal as a general absorbent and a tall column sand, you're going to get some pretty clean water out of the bottom.

John pretty much nailed it. My addition is store the water in the dark until used. If the container is opaque, paint it to keep the light out.