I have a twelve and a half year old belgian shepherd cross border collie. She's a sweetie, still thinks she's a pup and is very healthy, despite having severe malassezia which vet after vet haven't been able to resolve.
She has one problem, which is she climbs our greengauge tree, picks the fruit off and eats it. 
We normally fence it off before it fruits, but it caught us unawares this week, as its the other end of our long garden and we only realised it was fruiting when we saw her climbing it.
Since then she has once thrown up a small pile of greengauge stones. She seems fine in herself, no tenderness to her abdomen or throat, normal behaviour eating and passing stools ok.
BUT, she is behaving really strangely around her water bowl. We have one of those non-spill bowls and she usually lets us know its empty by grabbing it with her paw and kicking around the kitchen. Heard her do this last night, went it and she'd tipped the entire bowl upside down and it was full of water - so the floor was swamped. Since then she keeps on doing it. She looks like she wants to drink, looks at her bowl, then puts her foot in it and tips it up. (She looks anxious when she does this.)
I did try giving her a different (open topped) bowl with some water in and she took a couple of laps, but then went back and tipped up her own bowl again. I tried holding it up for her, just in case her throat was sore - but still no joy.
I put water in one of her stainless steel food bowls this evening after she ate and she did the same thing with that, only this time she actually put her foot in the middle of the bowlful of water. 
Initially I was concerned she might have either scratched her throat with one of the stones, or worse had one lodged - but this is contradicted by her eating two full meals perfectly happily. I don't think she can have eaten enough greengauges to cause an impaction and anyway she's still passing normal stools.
I am stumped. Bearing in mind the absence of any physcial symptoms, I'm now thinking it must be behavioural - but why? The only think I can think of is that we had a slug in the kitchen yesterday and I'm wondering whether it might have gone in the water bowl at some point and that's what's bothering her - but I assume if that were the case she'd be happy to drink from a different water bowl. (Her bowl has been washed up and refereshed several times since we evicted the slug infiltrator, so its not like its contaminated or anything.) She does look like she's peering at or into the water each time she does it, but she's by no means a fussy dog and has happily guzzled the water many times in the past, only for me to discover a piece of one the dc's dinner in there afterwards.
Has anyone seen anything like this before? I am at a loss to know what to do, but will try the vets in the morning if the behaviour doesn't settle down.