Proof that Water Pets are supposed to have significantly increased health regen:

[Dolalin]

Here's the water pet info page from magecompendium.

Problem is, it was captured in 2004 and the pet graphic is a luclin elemental, so the stats are probably significantly out of era.

However, it has very firm numbers.

Water pet regen is shown as 6hp/tick up until 39, where it hits 30hp/tick.

http://web.archive.org/web/200408080...r-library.html

This is exactly in line with other pets. Seemingly they are all the same according to the magecompendium all-pets chart:

http://www.magecompendium.com/library/oldpetchart.html

Now, all this being said, it is very possible these numbers were tnkered with over the years before magecompendium gathered them. But if I was a betting man I'd say P99 is using these numbers right now since they're clear and authoritative.