I don't have Jigokudo, but it may be intended like that. Water main has a passive called "Soul Absorption"
It works the same as Jigokudo's passive Soul Absorption and like Jigo, water main's only gives 10 chakra points and of course 10% life back..

The only ninja i know that gives 20 chakra back on unit death, is Orochimaru with his ambition passive.