what's the water simulation algorithms underling？

[GUI-Graphics]

very impressive！！after playing it many times，i decide to learn the code carefully。it will be painful without ideas or algorithms guidance。 the most mysterious is how you simulate water。i am not sure you use terrain simulation，or more complex theory like Navier-Stokes equations。can you give me some reference on water simulation，please？

[GUI-Graphics]

any tutorial， books or papers not very hard for beginners you would like recommend？or can you simply describe your water simulation algorithm，or give some keywords i can search？sorry for my poor english，thanks very much for reading。and have nice weekend。