quick startup questions floo/drain

Hey guys, have any of you kept resevoirs in basements/cellars and then pumped the water up a floor or two? How strong are these pumps, and can res. water be contaminated in a basement?

Also, I believe I read that an ebb resevoir needs to be replaced with a new resevoir of water every couple weeks. If we continually add water+nutes to the resevoir, what is the point of replacing the resevoir water alltogether? That is, isn't it contantly being updated with "fresh" water anyways?

One more thing: Are we wasting a lot of water this way (especially if using a large reservoir)? Like, if you had a 50gal res, then you'd be dumping out 50 gals of water every week? (or 2 weeks?)