Swimming % Increase Rule (10%?)

Definately more than 10%.  I don't know how much increase is safe but I jumped pretty quickly.  Since you don't have the pounding like running you can increase much more quickly.

I definitely think you could increase more than 10% and still be safe.  I recently hurt my knee and with a HIM coming up I was desperate to maintain fitness so I decided to just swim till I puked.  I just went from averaging swimming 2-3 times a week and about 5,000 meters a week, to doing a couple of weeks of swimming 5-6 times a week and about 15,000 meters a week.  I am not suggesting you should try this, but I had no issues.