I think even the slowest-acting of water critters won't cause any effects until 7 days, so wait and see. After 10 days and no effects, you can rejoice.
For those "oops!" cases, I have a 0.75 oz. McNett survival straw, an $8 water filter that you drink through, in my kit all the time. I've never used it in the field, but I bet with some fannagling someone could rig this as a main filter. Only good for 20 gallons or so. I also carry a few tabs of MicroPur, just in case.
If the water will be clear and free-flowing, I use the (original) Steri-Pen with the pre-filter (connected to a 1L Nalgene Cantene). With 4 lithium batteries, it weighs 7 oz. (Although the Adventurer is smaller and 3 oz. lighter, I couldn't justify the switch.) I carry a dozen MicroPur tabs as backup.
If the water will be icky and murky, or if there's the chance of herbicide/pesticide runoff, it's back to the General Ecology First Need filter. At 16 oz. it's as heavy as they get, but I swear this thing can turn nuclear sludge into Perrier. I've never had the filter weigh more than 16 oz. even after heavy use, so it doesn't hold water as is purported of other filters.