Repotting water lilies on a yearly basis is going to do more harm than
good. Lilies don't like their roots being disrupted at all... It sets
them back at least a month to redevelop feeder roots and start forming
new foliage. I'd say never repot ever, until either:

1) A rhisome is smothering the whole pot and domes up piles of foliage
which spoils its appearance and smothers it's own buds

2) Odorata type rhisomes get long leggedy and wander well out of the
pot

Helvola has a rhisome habit which clusters upwards, unless they are
growing into shallow water likely to freeze, I'd be inclined to let
Helvola thicken up for a couple of years, maybe snap off long crowns
that start to wander into open water, for new positions

The idea of stones on the top of the pot is to keep fish from
rummaging around with the lily pots soil, stones should be big enough
to stop fish pestering the soil, but not to cause such an obstacle to
the rhisome spreading across the pot...

Regards, andy
http://www.members.aol.com/abdavisnc/swglist.html

My questions
is should I re-pot it now, or do I even need to re-pot it at all? By
re-potting I mean the the place where I bought it sold my some clay
and said it should be done every year. And I placed river rock on the
top of the pot, should I do that? I read somewhere that that isn't a
good idea, I don't know why.

Thanks,
Gary