I think what is important is the fact that they would not know if it had forensic value without examining it. And this would go for anything else at all they might find.
As far as the water bottle might go, I would imaging they would want to examine contents and create a flow chart from there. What if it contained poison? Or a high concentration of medication? If yes, who put it in the bottle? Who injested it? And so on.
Or, as someone suggested already, if this was GPs , does it indicate GP was left with no water, if a later claim was made about her status when BL left her. I think it needs to be remembered, that the skull remains had not been identified as BL when the area was canvased.
Just that alone makes me think they would have bagged and tagged everything. This could have been a completely different investigation.
Well, then, truly, they should have excavated the entire pond area and taken out bags and bags of sludge. All of that is far more likely to indicate cause of death than the water bottle. But they didn't - I believe it's because CoD might have been fairly obvious.
No one I know who does forensic investigation would have operated off the assumption that a body found in that place, with several items of Brian's nearby, was anyone but Brian - all the dental evidence did was confirm it legally. LE are not ignorant nor willfully negligent, they knew who it was, with near certainty.
And again, all of the organic matter under where the bones were found (down to a depth of say 3 feet) would be good evidence - but they didn't take that either. I think it's because they had a pretty good idea about CoD. They just aren't sharing that until they get the forensic anthropologist to weigh in on things like how much force it took to blow the skull apart (without the anthropologist knowing what weapon was found - because that's not how things go in a forensic investigation; anthropologist must work separately). If the anthropologist says, "Sure looks like a single gunshot wound, at point blank or near point blank firing, with X lbs of pressure exerted at the top of the skull and the entry point being at the back of the lower jaw" (I'm just making this up - but that's the kind of thing we anthropologists weigh in on), and then LE has a gun that is capable of that injury - they're going to say CoD is a gunshot wound, even if they didn't find the bullet.
Sure, they can go back and excavate an area of several acres looking for the bullet, or they can take a bunch of sludge out of the pond looking for a casing, but...do they need to in this circumstance? If so, why isn't every single crime investigated in this manner - each one costing upwards of $6M, which is about where the bill is for this one, right now.
Meanwhile, crimes all over the US get little attention and far less expenditure. Gabby and Brian are both dead. Tips will be followed up, but there are no other suspects or POI's. If someone hated both of them enough to follow them all around the US, killing them at separate times and staging a suicide, well, that's a first in the legal and forensic annals, and...we will probably never know the "true killer."
Me. personally, I'm going to go with what the coroners say. Always room for error, people can continue to believe many things about this case, but I do hope both families are left in peace, because their grieving process has only just begun. I also pray that no further harm comes to any of the family members or LE or attorneys involved in this case.