
I can remember years ago my Mums cocker and my own drinking a puddle dry in a local park, they were off lead and playing hard and kept going back for another slurp till all the water had gone,never thought about them picking up any bugs, they then marked every tree and lamp post on the walk home.
If it was stagnant water I would be more concerned, my dogs have drunk canal water,even lost their balance and fallen in on each occasion, bar for needing a bath they didn't come to any harm.
I think the acid in their stomachs kills off most bugs unless they were in huge numbers.