If you're feeling smug by refilling your water bottle several times a day, think again.
While H2O does wonders for the body, re-fillable bottles that aren't washed regularly can be cosy havens for bacteria.
According to a recent study, bacteria levels on water bottles can reach similar numbers to those found in a toilet. But if course, the difference is you aren't putting your mouth near a toilet bowl.
The study, by treadmillreviews, looked at reusable water bottles after each had been used by an athlete for a week.
The bottle with the most bacteria came in at more than 900,000 colony forming units per square centimetre - which is more than the average toilet seat.
While most of the bottles tested came in at a much lower 313, 499 CFU per square cm, that's still a lot of germs to be putting in your mouth.
As if that isn't gross enough, researchers also found that 60 per cent of the germs commonly found on water bottles are the kind that can make people sick.
And when it comes to the type of water bottles being used, some can be more germ-ridden than others.
Researchers found slide-top bottles harboured the most bacteria by far, at 933,340 CFU per square cm. Squeeze and screw-top bottles came in second, at about 160,000 CFU per square cm, and straw-top bottles were the cleanest, at around 25,400 CFU per square cm.
Just to put it into perspective, a pet bowl typically has about 47,300 colony-forming units of bacteria per square cm, the kitchen sink has around 3,190, and you toothbrush holder can be a bacteria hotspot too, with about 331,800.
According to Metro UK, the reason why water bottles get so nasty is that people simply don't wash them enough.
While reusuble bottles are the most environmentally choice, they should be washed every day, either by hand or in the dishwasher.
And choose a stainless steel bottle, which is less of a magnet for bacteria than the plastic variety.