Im looking into this for you. But my results wil be a bit "piece-meal"
as I am getting often interruped right now.
Feel free to ask questions about anything I say / fix at any time.
Firstly, debug is failing (intermittantly but often) because your
"source" and "dest" arrays are defined wrong.
Youve defined them both with "19" columns/rows, but you are writing to 20.
(element 0 is the first, through to element 19 is the 20th)Change their declarations to
var dest[20][20];
var source[20][20];and that problem is repaired.
Im doing some general lite-c optimisations while Im in here too.
This code looks like either you based it on an old c-script code,
or that YOU are more familiar with c-script than lite-c.
Either way, these improvements should help you grasp lite-c better.
(and make it easier for ME to debug your core code problems 
)[EDIT]
...This code looks like either you based it on an old c-script code,...
Not that Im saying you based it on someone-elses work,
but that youve used an old mesh-deformation c-script to put your water-physics onto.
