Neither string floss nor a water flosser has proven categorically superior for a healthy mouth with no dental work. Cochrane finds that cleaning between the teeth, on top of brushing, reduces gum inflammation whichever tool performs it.1 Water flossers have the stronger case around braces, bridges, and implants.2, 3 The best interdental tool is the one you'll actually use every day.
Why is this comparison unusually careful?
Because a large share of the published studies on water flossers were funded by the companies that make them: the one thing worth knowing before comparing the tools. That doesn't automatically make the findings wrong, but it's why the boldest comparison claims you'll see in ads don't appear on this site. Everything below leans on independent evidence: Cochrane reviews and peer-reviewed studies without a manufacturer holding the pen.
What does the strongest evidence agree on?
That cleaning between the teeth, on top of brushing, reduces gum inflammation, whichever tool performs it. That's the common ground, and it's the most important finding of all. Cochrane, the international body widely considered the gold standard of medical evidence review, reaches that conclusion for gingivitis, the earliest stage of gum disease.1 The certainty is modest and the direction is consistent.
The evidence supports the habit more strongly than it supports any particular tool.
In other words: the biggest measurable difference isn't between string flossers and water flossers. It's between people who clean between their teeth and people who don't.
What's the case for string floss?
String floss is the tool with the longest evidence trail, and it's the one most of the large observational findings on this site are built on: the same Cochrane review above includes flossing among the interdental methods linked to reduced gum inflammation.1 It's also cheap, portable, and requires no charging or countertop space. Used with decent technique, it physically wipes plaque off the sides of the teeth, a mechanical action a water stream doesn't replicate the same way.
Its honest weakness isn't in the lab. It's that many people find it fiddly, and two out of three American adults never made it a daily habit.
What's the case for the water flosser?
Independent evidence supports a promising but limited signal, and it deserves to be stated at exactly that strength. Adding a water flosser to brushing has been shown in some controlled studies to reduce early gum inflammation, though researchers note the evidence is still limited: the same Cochrane review graded the certainty of that finding as very low, and a benefit visible at one month was no longer detectable at three.1 That is a genuinely promising signal, honestly labeled, not an established fact.
Where the water flosser's case gets stronger is dental work. For people with braces, implants, or bridges, a directed water stream reaches areas string floss physically can't, and studies show it helps control gum bleeding around implants and brackets: a 2025 systematic review of oral irrigators and a 2025 randomized controlled trial both point the same way.2, 3 The honest caveats: these are small studies with follow-up of six months or less, so certainty is low. We cover this scenario in depth in flossing with braces, bridges, and implants, and the technique itself in how to use a water flosser.
Which claims won't you find here?
The dramatic head-to-head superiority numbers, in either direction. If you've shopped for a water flosser, you've seen them. Those figures come from manufacturer-funded marketing studies and haven't been independently verified, so we don't repeat them, in either direction. The same goes for claims about which tool people stick with longer: there's no independent evidence on that question at all. When the honest answer is "we don't know," that's the answer this site gives.
So which one should you use?
The one you will actually pick up every day, which is the thing the tool debate keeps missing. Government survey data shows only about 1 in 3 US adults report flossing every day. And since that's self-reported, the real number is likely lower.4 The real-world problem was never which tool wins in a lab. It's which tool people will actually pick up and use.
So the honest comparison ends like this: string floss and water flossers both have independent evidence behind them, each has situations where it shines, and neither has proven itself categorically superior for a healthy mouth with no dental work. The best interdental tool is the one you will actually use every day. If string floss has sat unused in your drawer for years, the tool that finally gets you cleaning between your teeth daily (whatever it is) beats the theoretically better one you never touch.
Common questions
Is a water flosser better than string floss?
Not categorically, on independent evidence. Neither tool has proven superior for a healthy mouth with no dental work. Cochrane graded the water-flosser gingivitis finding as very low certainty, and a benefit visible at one month was no longer detectable at three.1 The habit of cleaning between the teeth has stronger support than either tool.
Can a water flosser replace string floss?
The independent evidence doesn't establish that it can, and doesn't establish that it can't. String floss mechanically wipes plaque off the sides of the teeth in a way a water stream doesn't replicate. That said, if string floss has sat unused in a drawer for years, the tool that finally gets you cleaning between your teeth daily beats the theoretically better one you never touch.
Which tool is better with braces, bridges, or implants?
The water flosser has the stronger case there. A directed water stream reaches areas string floss physically can't, and studies show it helps control gum bleeding around implants and brackets. A 2025 systematic review and a 2025 randomized controlled trial both point that way, with the caveat that these are small studies with follow-up of six months or less.2, 3 More in flossing with braces, bridges, and implants.
Why doesn't this page quote the big head-to-head superiority numbers?
Because those figures come from manufacturer-funded marketing studies that haven't been independently verified, so this site doesn't repeat them in either direction. The same applies to claims about which tool people stick with longer: there's no independent evidence on that question at all.
Does it matter how often I use whichever tool I pick?
Daily use is the standard the evidence is built on, and consistency is the variable that actually moves. Government survey data shows only about 1 in 3 US adults report flossing every day, and because that's self-reported the real number is likely lower.4 If the habit keeps slipping, why people quit flossing covers what actually helps.
- Worthington HV, et al. Home use of interdental cleaning devices, in addition to toothbrushing, for preventing and controlling periodontal diseases and dental caries. Cochrane Database of Systematic Reviews, 2019, CD012018. Cochrane CD012018. Water-flosser gingivitis finding graded very-low certainty.
- Systematic review of oral irrigators and periodontal outcomes, 2025. PMC11779913. Small studies, follow-up ≤6 months.
- Randomized controlled trial of dental water-jet use, 2025. PMC11855567. Small trial, short follow-up.
- Fleming EB, et al. Prevalence of daily flossing among adults, NHANES 2011–2014. Journal of Periodontology, 2018. CDC authors. PMC6434526. Self-reported survey data.