You've got to remember that that level was made as an easier version of a harder level. The harder version gives you no builders (and is in fact otherwise identical - same lemmings, same %, same time, same release rate, same skills except for 0 builders, thus showing how evil I can be - no hints towards which skills are used), and all water that can be accessed without builders does indeed work as normal.
That's also part of the reason why it's 30 lemmings. 80 lemmings and 20 floaters would be assumed as normal for a x-of-each-skill level. 30 lemmings and 20 floaters, in a 100% level where floaters are useful, is just plain evil. (I even considered making it 21 lemmings, just to be extra annoying, but decided against it in the end.)