Start with the interruption most likely to make you skip the device. If a refill breaks the routine, published reservoir capacity matters. If permanent counter space is the bigger obstacle, a smaller cordless tank may still be the better buy.
This guide compares current published reservoir information for the Waterpik WP-660, Waterpik WP-580, and Philips Sonicare HX3711/20. Waterpik publishes seconds ratings for both of its current pages; Philips publishes a 550 ml tank and says it holds enough water for more than one session. Those are manufacturer statements, not our stopwatch tests.
Start with the interruption that breaks the habit
A larger tank is useful only when it removes a real point of friction. Some buyers would rather refill once than live with a base, hose, and power cord on the counter every day. Others know that one interruption is enough to make the device sit unused after the first week.
That is why reservoir size belongs in the routine-fit column rather than the clinical-results column. The ADA's evidence summary describes oral-irrigator evidence as limited and inconsistent, so a bigger tank should not be treated as proof of better health outcomes by itself.
- Prioritize published capacity when uninterrupted use is the difference between using the device and skipping it.
- Accept a smaller tank when storage, travel, or shower use matters more than one refill.
- Treat reservoir size as a friction variable, not a promise of superior results.
What the current published numbers actually say
Waterpik lists the WP-660 with a 651 ml reservoir and a 90-second capacity rating. It lists the WP-580 with a 207 ml reservoir and capacity of up to 45 seconds. Philips lists a 550 ml tank for the HX3711/20 and says it holds enough water for more than one session.
Those numbers are comparable only up to a point. Waterpik gives both milliliters and time ratings on the current pages. Philips gives the tank size and a broader usage description, which is useful but should not be converted into an exact runtime the page does not publish.
- WP-660: the biggest published reservoir in this three-model set.
- WP-580: the smallest reservoir and the clearest refill tradeoff.
- HX3711/20: a mid-sized published tank with a broader session-length description.
Which setup each reservoir favors
The WP-660 is a corded countertop model for North American 120V/60Hz outlets, so its 651 ml reservoir makes the most sense when the device will stay in one bathroom and longer uninterrupted use matters. The Philips HX3711/20 is also a countertop model, and its 550 ml tank targets the same general pattern: permanent placement in exchange for less refill friction than a cordless body usually provides.
The WP-580 takes the opposite approach. Waterpik describes it as waterproof, shower-usable, rechargeable, and globally voltage-compatible, with travel accessories in the box. Its smaller 207 ml reservoir is part of that portability package rather than a defect to judge in isolation.
- Countertop fit: WP-660 or Philips when you can leave the system out and ready.
- Travel or small-bathroom fit: WP-580 when portability matters more than maximum tank size.
- Do not pay for extra capacity you will not use because the format itself is inconvenient.
The refill tradeoff people miss
Refill friction is not only about published seconds. It is also about how you fill the tank, whether the reservoir is easy to remove and dry, how much weight sits in the hand during use, and whether the device has a realistic storage spot afterward.
A countertop tank can reduce interruption but increase visual clutter and cleaning steps. A cordless body can disappear into a drawer or travel bag but place the tank and motor in one hand. The right comparison is the nuisance you are actually willing to tolerate every day.
- A larger tank does not solve cord management, drying, or counter footprint.
- A smaller tank does not automatically mean a poor fit if the device is easier to store and charge.
- Session length can vary with setting and technique even when a manufacturer publishes a capacity figure.
Check the exact page before you buy
Use the official model page to confirm the precise package, included tips or nozzles, charger details, power requirements, warranty language, and replacement-part availability. Similar family names and retailer listings can hide meaningful differences between configurations.
If braces, implants, bridges, crowns, pain, or persistent bleeding are part of the decision, ask a dental professional which tip and interdental-cleaning method fit your situation. This article covers published specifications and routine tradeoffs, not individualized dental advice.
- Match the exact model number before trusting a comparison table.
- Check the seller's return window so setup friction can be evaluated at home.
- Verify replacement tips, replacement tanks, and charger compatibility before checkout.
VERIFIED PRODUCT LINKS
Check the exact models
SOURCES & SCOPE
Trace every factual edge.
Product specifications are manufacturer statements unless explicitly labeled otherwise. General oral-health context comes from the ADA. This page provides general information, not individualized dental advice.
- Waterpik — Aquarius WP-660 official specifications
- Waterpik — Cordless Advanced 2.0 WP-580 official specifications
- Philips Sonicare — Power Flosser 3000 HX3711/20 official specifications
- American Dental Association — Dental Floss/Interdental Cleaners evidence summary
Registered claims used on this page
ada-evidence-limits— Do not imply that all water flossers, techniques, or users will have the same outcome.wp660-use-profile— Do not describe this North American model as globally voltage-compatible.wp580-travel-specs— The official page says the magnetic USB-A charging cable is included but a wall adapter is not.philips-tank-spec— Keep the claim to the listed tank capacity; do not promise a specific session length for every user.wp660-capacity-spec— Attribute the figures to Waterpik; actual session time can vary with setting and technique.wp580-capacity-warranty— Attribute the figures to Waterpik; actual session time and warranty coverage depend on use, region, and current terms.philips-session-warranty— Attribute the figures to Philips; actual session length and warranty coverage can vary with use, region, and current terms.