Originally Posted by flyabq
Yes, Water has a much higher surface tension than 100LL. While it might not leak with water it doesn't mean that it is still 100% leak proof. You would be much safer to do the final test with either properly regulated air or 100LL.
The initial test with Water should be fine to test for larger leaks. If there are any of descent size then water will still leak.
Without pressure, solvents, such as gasoline, can easily weep through spaces that water cannot, due to the lower surface tension.