Oh and as for the lootgroup question, I can see situations where I would want to add an item specifically to dilute the pool (in another mod I'm fiddling with, I want there to be more garbage-y food items besides just rotten meat and sham sandwiches), but in others I can see wanting to make sure it's additive and not reducing existing droprates. In those cases you would add a new lootgroup, correct? So the original lootgroup chances for a given container are unchanged but now there's an additional possibility of finding something from the new lootgroup?
As far as the water mod goes, I'm planning on adding buckets to a great many containers. I don't think dilution will be a huge issue as I'm shooting for them to be roughly as easy to find as cooking pots, which are probably uncommon enough to not flood the containers I'm targeting.
Then again, I'm not sure if altering the lootgroups that buckets are currently part of is a better idea than adding a new lootgroup just for additional buckets.
EDIT: Spent some time going through all the lootgroups, and am putting together alterations I hope to add for that aspect of the mod, adding buckets to some lootgroups, but also directly to some containers, making them variously available in sinks, garage and farm containers, firetrucks, and irregularly in a couple other places (e.g. dumpsters). Hopefully this will work out well enough for them to be available in (mostly) intuitive locations and in sufficient quantities/frequency.