Lego is not water-tight, but Aqua Lego is! This is achieved by having each item in a set of available as both "male" and "female" parts.
The male parts have rubberised grommets running around their perimeters, and the matching females have corresponding grooves to accommodate them, ensuring a watertight seal when the pieces are pressed together.
This naturally makes Aqua Lego an expensive choice as every piece must be doubled up, and more carefully engineered, but ships and all sorts of other floating constructions or even dams are now possible.-- xenzag, Sep 08 2009 WaterWall http://www.gizmag.com/go/2795/picture/94/ [Klaatu, Sep 09 2009] "females have corresponding groves" - a grove of trees, for example?-- hippo, Sep 08 2009 grrrrr... ha ha - (fixed!)-- xenzag, Sep 08 2009 Not sure I understand the male-female thing - isn't each bit of lego ("a lego" - if you will) already hermaphroditic? Couldn't you do the rubberisation as is, without having to have explicitly male and female variations of the same bricks?-- zen_tom, Sep 08 2009 Need it.-- 2 fries shy of a happy meal, Sep 08 2009 Obligatory WIFRT: I thought it was proposing a new colour for Lego bricks...
You don't indicate how you plan to get your watertight seal on the ends of your Aqua Lego pieces. I would think that's where the worst of the leakage will occur. Tongue & groove, perhaps? Or fabricate the Aqua Lego blocks out of silicon rubber so they will tend to cling to each other, sort of self-sealing?-- Canuck, Sep 08 2009 Having valve bricks and Technic sealed bearing holes might stimulate some unique wet builds.-- wjt, Sep 08 2009 Just a tiny gasket layer on the base of each piece would create air pockets.-- 2 fries shy of a happy meal, Sep 08 2009 Aqua Lego has a ring to it. It sounds like someone's name.-- bungston, Sep 08 2009 I'm travelling at the moment... will illustrate idea when I get back. It's quite simple, and I think would work fine.-- xenzag, Sep 08 2009 like it!-- dentworth, Sep 08 2009 I didn't know that normal lego was not watertight. I suppose I never did test it. This is definitely necessary then. [+].-- jellydoughnut, Sep 14 2009 random, halfbakery