My son first saw the Hydrodynamic Building Set by Bridge Street Toys at a museum five years ago.  He has always enjoyed plumbing, piping, and pool pumps.  Thus, this was an immediate hit.  We found a set online via amazon and put it on his wish list in 2012.  His grandparents got it when it was on sale.  It was truly the perfect find!

I have to admit, this set is extremely hard to find.  In addition, it is expensive for a building set.  Our son is lucky his grandparents got it when they did 4 years ago!  It appears to only be available from Bridge Street Toys now.

That being said, it is a very unique building set.  It is the only building set that I have seen that lets children learn about hydraulic engineering.  It comes with a submersible pump and tubing along with lots of building materials to construct a variety of tanks, funnels, and chambers.  The guide is extremely basic in that it does not give step-by-step building directions but rather pictures of projects such as a toothpaste factory, paint pilot plant, vinegar production facility, distillation tower, ice cream factory, etc.  However, the kit is extremely easy to free-build any type of water distribution creation.  In addition, the guide does give an explanation of the components and how they would be used in real-life.

Here is a neat video of the set done by a dad and his two boys.  In their video, they used the kit outdoors.  We have been using ours indoors, but with lots of towels around.  It is fun but will get water everywhere depending on the creation or fiddling while operating by your child.  It is definitely a great outdoor water toy, but with towels on hand, it can be inside.

The recommended age is for 10+ but that is solely because of some of the small parts and construction is not the easiest.  My son is 9 and when he first got this kit years ago he needed lots of adult assistance.  Now he only needs a little help but is mostly independent.  In addition, the lack of step-by-step directions will frustrate younger children.  However, if an adult or older sibling is willing to help, the kit would be perfect for younger elementary age students.  The kit is not only fun but has great educational potential.

If you can find one of these sets, it is definitely a lot of fun!