Found this neat project by Oliver Kreylos, and gave it a go over a weekend using only spare parts.
It came together well on a Toshiba i5 laptop. I found there to be issues using the Intel graphics card/drivers, so I swapped to an AMD Athlon 2X4 with a Radeon HD47## card (no longer supported by AMD). It did refresh faster than the Intel graphics card, but had the same ‘unknown’ issue when trying to render water. After swapping out the Radeon with a slower Nvidia card, it all displays correctly, but the frame rates where pretty slow. I reduced the quality of the water and the frame rates have increased.
With a working model, I decided to upgrade from the test cardboard box, speaker stand and copious amounts of quick release clamps. The sandbox and stand has been rebuilt in spare wood.
The following week I realised that the ambient light from the sun was interfering with the Kinect, so it was moved into the shed.