Ooh, lucky you! My favourite WF pool is Larkswood Leisure Centre in Chingford - lovely and new / clean. Otherwise in/near Walthamstow it's Leyton Leisure Lagoon (fun with nippers, but a bit scummy really) or Walthamstow Pool & Track (nice size, bit grubby/tired). Both the latter two have seen better days, I reckon, but fine if you don't think too hard about hygiene/concentrate on chlorine! There's another pool in Leytonstone which I think is meant to be rather nice. Enjoy!