daniel b, i also play waterpolo (only womens nat league) if you still do that at all it's not too compatible with running if you get any knee problems becuase of eggbeater (I had to lay off the polo during mara build up because of tendon strain). I swim or polo 5 x week, but don't need to leave any space between a swim day and a run day, diff sets of muscles (am lazy swimmer, work off my arms more than legs). Obviously there is general tiredness to combat, and on the days after a long run(2+ hours) tumble turns could give a cramp twinge as i push off, however for the most part I find swimming allows a training day where I would otherwise need a recovery day - ie if you run on a sunday (and if you are still building a running base) you'll probably feel sore on the monday and don't want to run or gym, however I feel swimming actually helps muscle recovery, and means you don't need to take too many rest days.
Avoid tough kick sets the day after though until your legs get used to the running a bit more.
As long as i take 1 rest day a week all is fine generally. You'll probably find with running your aerobic fitness is great and for now it's your leg fitness which restricts you. Don't push too much too soon though.
If i were you I'd run tuesdays and saturdays to start with (dunno how far you currently run or for how long). As you get fitter for running you can add another run a week, I do run and swim on same day sometimes with no real problem (although not much at the mo due to time restrictions). This way you can keep 1 or 2 rest days a week. It also allows you to lengthen the saturday run when you feel ready.
