The tanks in the 77 are the same system as used in the Astir Cs.
I operated Astir Cs for many years and flew with water regularly. There is
also one in our club that I have to do maintenance on some times.

Considering that the tanks are just forward of the main spar I think that
the danger with a leak is that the water will leach into the structure and
weaken it.
In Australia there is a general Airworthiness Directive for all fibreglass
wing tanks that they must be leaked tested each year. The relevant one is
AD165.
I know that there has been several tanks found to be leaking using this test
and many have been repaired using several methods. Some repair methods are
less successful than others. Some have been Astir and others have been
Jantars and a Mosquito so the problem is not just on the Astir.

"pete83" wrote in message
om...
As i know the astir cs-77 has integral-water-tanks. How likely is it
that the construction is leaky and water can reach parts of the wings
where it can't flow off again? What could be happend if the tanks
would be leaky ?