Water flosser vs string floss: what the evidence says

Oral Cove editorial deskUpdated September 2026Every figure below is traced to the source listed at the end
Short answer

There is no single winner. For plaque between tight contact points, floss and interdental brushes have the more consistent evidence. Water flosser trials often look better on bleeding, including around implants. Cochrane 2019 called the irrigator evidence limited and inconsistent, so the answer depends on which outcome you measure and which tool you will actually use daily.

If you search this question you will find two camps, each quoting a different trial. The trials are real. What usually goes unmentioned is which outcome was measured, how long the study ran, and who paid for it.

On this page
  1. Outcome by outcome
  2. What Cochrane actually concluded
  3. Follow the funding line
  4. Where each tool wins
  5. A decision rule that survives
  6. Questions people ask

Outcome by outcome

This is the whole comparison in one table. Read the outcome column first, then the source, because the two tools do not lose or win overall, they lose and win on specific things.

Outcome measured Water flosser String floss or interdental brush Source
Gum inflammation at one month May reduce it (4 trials, 380 people), very low certainty Floss may reduce it (8 trials, 585 people), low certainty Cochrane 2019
Gum inflammation at three and six months No effect shown Floss still showing a reduction at three and six months Cochrane 2019
Bleeding sites No advantage over toothbrushing alone No clear advantage at one or three months; one small effect at six months in a study at high risk of bias Cochrane 2019
Plaque No advantage over toothbrushing alone at one, three or six months Interdental brushes reduced plaque more than toothbrushing alone, and may beat floss Cochrane 2019
Implants, bleeding at 30 days 18 of 20 implants improved, against 6 of 20 in the floss group 6 of 20 implants improved Mahajani 2024, single centre, 40 implants
Fixed braces, two weeks Plaque down 21.9% and bleeding down 32.3% from baseline Plaque down 16.1% and bleeding down 23.6% from baseline, no statistically significant difference between groups AlMoharib 2024, 30 participants
Gum tissue abrasion over four weeks No difference from an interdental brush No difference from a water flosser Mancinelli-Lyle 2025

What Cochrane actually concluded

The 2019 Cochrane review is the strongest single reference on this question, because it pooled 35 randomised trials and 3,929 adults, and it was produced without device industry funding. Its summary on oral irrigators, stated plainly:

  1. Adding water irrigation to toothbrushing may reduce gingivitis at one month, on very low certainty evidence.
  2. That effect was not found at three or six months.
  3. Irrigation showed no reduction in bleeding sites and no reduction in plaque compared with toothbrushing alone.
  4. Comparison with floss gave low to very low certainty evidence that irrigation may reduce gingivitis at one month.
  5. Interdental brushes may reduce gingivitis more than floss at one and three months. The effect sizes overall may not be clinically important.
The limitation nobody puts in the headlineMany participants in these trials started with a low level of gum inflammation, and the outcomes were mostly measured at one to three months. No included trial measured decay between the teeth, and very few measured periodontitis. So no study here can tell you that switching tools will change what your mouth looks like in ten years.

Follow the funding line

The water flosser trials are mostly industry studies. The 2025 trial that found a water flosser beat an interdental brush for marginal gingival bleeding over four weeks lists the first author as an employee of Water Pik, Inc. at the time of the study, with the study commissioned through a research company that received financial support from Water Pik, and products supplied by Water Pik. The 2024 implant trial used a Waterpik device. That does not make the results wrong, and the trials were designed and reported to a reasonable standard. It does mean that when a water flosser study and an independent review disagree, the independent review should carry more weight.

This is also why the honest comparison is not a scoreboard. The trials that favour water flossers tend to measure bleeding over four weeks in a specific group of patients. The Cochrane review measures everything it can find across 35 trials and rates the certainty down accordingly.

Where each tool genuinely wins

Worth it if

  • Braces, wires and fixed retainers, where floss has to be threaded around hardware
  • Implants, crowns and bridges, where the trial evidence favours irrigation for bleeding
  • Hands that cannot manage floss reliably, or wrists that tire quickly
  • Anyone who has been told their contacts are too tight for an interdental brush and who will not floss

Skip it if

  • Tight contact points where nothing but floss will physically pass
  • Plaque between the teeth, where interdental brushes have the best record
  • Travel, because a box of floss costs a few dollars and fits in a pocket
  • Gaps that a correctly sized interdental brush passes through, which is most adults at some sites

A hygienist can size interdental brushes to your gaps in one appointment, and they are one of the cheapest dental tools there is. Our own store sells interdental brushes and floss picks from $5, next to water flossers from about $10 to $70 and replacement nozzles from $5 to $9.

A decision rule that survives the uncertainty

  1. If you have gum disease or your dentist has measured pockets, ask which interdental tool they want you to use. Professional measurement beats any comparison table, including this one.
  2. If a correctly sized interdental brush passes between your teeth, use it, and add floss only at the tight sites where it cannot.
  3. If you have fixed braces, implants, or cannot manage floss, choose the water flosser and use it once a day at a pressure that stays comfortable.
  4. Whichever you choose, brush twice a day for two minutes with fluoride toothpaste and do not rinse it away afterwards.
  5. Pick the option you will use every day. A well-evidenced tool that stays in the drawer loses to a decent tool that gets used. The routine builder turns this into a five-question answer, and the water flosser setup guide covers pressure, tips and order.

Related

Questions people ask

Is a water flosser better than string floss?
It depends which outcome you measure. Water flosser trials tend to look better on bleeding and gum inflammation, including around implants. Cochrane 2019 found interdental brushes had the more consistent record for plaque and gingivitis, and interdental brushes beat floss. No single trial has measured what most people actually care about, which is whether teeth and gums are still intact in ten years.
Can a water flosser replace flossing?
For some people, yes. If floss cannot get between your teeth, if you have braces or implants, or if your hands cannot manage floss, a water flosser is a reasonable daily interdental step. If your contacts are tight and you can floss or use interdental brushes, those tools still carry the better evidence for plaque removal.
Water flosser or interdental brush?
Interdental brushes have the better evidence for plaque and gingivitis, and they are cheap. But they only work in gaps a brush can enter, and a hygienist usually needs to size them for you. A water flosser reaches everywhere without a sizing step. People with both often use brushes in the wide gaps and the water flosser around the rest.
Do dentists recommend water flossers?
The American Dental Association accepts powered interdental cleaners, and Waterpik water flossers hold the ADA Seal in that category. Individual clinicians vary, and the ones who do not recommend them usually point at the low certainty of the irrigator evidence compared with interdental brushes. Ask your own dentist what your gum measurements suggest.
Does flossing stop tooth decay?
The gum-health case is stronger than the decay case. Cochrane 2019 found no trial that measured decay between the teeth, and the ADA reports that only regular professional flossing five days a week reduced interproximal decay in a meta-analysis, while self-flossing did not. Clean between the teeth for your gums; do not treat it as a cavity vaccine.

Sources

  1. Worthington HV, MacDonald L, Poklepovic Pericic T, 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 — www.cochrane.org/evidence/CD012018_home-use-devices-cleaning-between-teeth-addition-toothbrushing-prevent-and-control-gum-diseases-and
  2. Mahajani MJ, Kalla M, Sonkesriya S, et al. Comparison of the impact of two interdental cleaning devices on the reduction of bleeding around implants. Journal of Pharmacy and Bioallied Sciences 2024 — pmc.ncbi.nlm.nih.gov/articles/PMC11001108/
  3. AlMoharib HS, Alqasem A, Almusfer G, Aldosari MA, Almadhoon HW. The effectiveness of water jet flossing and interdental flossing for oral hygiene in orthodontic patients with fixed appliances: a randomised clinical trial. BMC Oral Health 2024 — doi.org/10.1186/s12903-024-04166-0
  4. Mancinelli-Lyle D, Van der Weijden GA, Slot DE. Efficacy of a water flosser compared to an interdental brush on gingival bleeding and gingival abrasion: a 4-week randomised controlled trial. International Journal of Dental Hygiene 2025 — pmc.ncbi.nlm.nih.gov/articles/PMC11717974/
  5. Barnes CM, Russell CM, Reinhardt RA, et al. Comparison of irrigation to floss as an adjunct to tooth brushing: effect on bleeding, gingivitis and supragingival plaque. Journal of Clinical Dentistry 2005 — pubmed.ncbi.nlm.nih.gov/16305005/
  6. American Dental Association. Dental floss and interdental cleaners: current recommendation and the flossing evidence — www.ada.org/resources/ada-library/oral-health-topics/floss
  7. NHS. How to keep your teeth clean: flossing, interdental brushes and fluoride toothpaste — www.nhs.uk/live-well/healthy-teeth-and-gums/how-to-keep-your-teeth-clean/

The tools in this comparison

Interdental brushes, floss picks, water flossers and replacement nozzles, all on one page.

See the range

Which one to buy

Every option this store stocks, with price, type and who it suits, is compared on one page.

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