Life-like water

1. Even the water surface by pouring a thick layer of polymer/nitrocellulose glue easily available from DIY stores. You may theoretically just use a PVA glue but then the base of your model may warp ruining the effect
2. Paint the water with a grey paint with a hint of green and blue. Darker in the middle with brighter shallow areas. I use Games Workshop's Shadow Grey

1. Cover the water with a glossy varnish
2. Use drybrush to paint some yellowish-green duckweed at the edges

I don't use ready-made modelling water as it is expensive and actually worse then a glue covered with varnish.