+1 to Montanero and Scafool. Also, it seems the filter wasn't designed properly because there are several stages missing. The first (top) layer should be gravel, then progressively finer sand. Next a layer of very fine mesh fabric or cotton wool, then a layer of charcoal (extremely important!) and another thin layer of fabric or cotton wool.

That's the kind of filter we were taught to build and it works fairly well for removing the major gunk though you'll probably still need to boil or chemically purify the water. Anyway, it's a pretty slow process. If there are enough stages and all the material is compacted down correctly, the water will drip out slowly, measured in drops per second! If it goes any faster than that, the filter is probably not working right.