there are different kinds of clear resin you can use for water.
All depends on what you want to make...
The 3 main kinds of resin are:
1-compounds water-resin (GW sells this...) which is good for putting a bit on the figure's base, to make a small waterfall, to create little waves etc on the water... It never gets completely hard, more soft, but still dry. I have a slight feeling it will turn rather yellowish during the years...
I think its pretty close to PVA-glue, only with a few more specific compounds to make it completely clear (as long as the coating stays thin enough) and glossy and just a lil more vicious...
2-compound water-resin (NOCH / ...) : easy to use, usually 1 part A + 1 part B, mixing well and cures in 24 hours (as they say... but it depends on how thick your coating is... I once did a 1 cm coating of this stuff in my dead marshes diorama... it took over 72 hours to cure completely). It gets hard though! But, easy to work with...
melting-pearls + additive (NOCH / ...): I used pearls to melt in my latest diorama (in the house of tom bombadil), great stuff! You need some more preparations though... You must heat it in a heat-resistant pot in your oven.. (kitchen will smell like a plastic-factory-lab), and treat it warm (following instructions of course...), you have to make sure everything which gets in contact witht he resin on your final piece must be resistant to that heat.
This is excellent for thicker coatings and so on! great stuff I think!
Gets hard in minutes (take at least an hour or two though)
I also use it to heat on a spoon above a candle and tap the melted stuff against a certain hangover on a display-base to create icycles... (like on a roof or something).
Another advantage of this is, you can always re-use it, leftovers can be melted again and again... If it gets scratches, you can fix it with heat (even with a hairdryer they told me, same counts for the 2-compound water-gel of NOCH)...
NOCH is great quality stuff for modeling and landscaping, here's a link to their stuff to give you an idea what kinds of water-resin you have...
http://www.noch.de/en/produktkatalog/listview.php?submenue=n&navi_Kategorie1=NOCH&navi_Kategorie2=Terrain+Forming+%26+Crafts&navi_Kategorie3=Landscaping&navi_Kategorie4=Wasser-Produkte&jahrNeuheiten=
There are of course many more suppliers around which are just as good (I just only used NOCH and Bush (1-compound resin) so far.)