A flush urinal uses water on every use (federal max 1.0 gpf, WaterSense models 0.5 gpf or less), while a waterless urinal uses no water and relies on a sealed cartridge that blocks sewer gas. Waterless saves more water but trades flush upkeep for scheduled cartridge service.
How does each type of urinal work?
A flush urinal works like a small toilet. A valve, usually a flushometer, releases a measured burst of water that rinses the bowl and pushes waste into the drain through a built-in water trap. That trap stays full between uses, and the water seal is what blocks sewer gas from rising back into the room. The flush also keeps the bowl and drain line rinsed clean. Most commercial flush urinals run on a manual handle or an automatic sensor that triggers the valve.
A waterless urinal has no valve and no flush. The bowl drains into a replaceable cartridge at the bottom. Inside that cartridge sits a layer of sealant liquid that is lighter than urine, so urine sinks through it and continues down the drain while the sealant floats back into place and seals the opening. That floating layer does the same job the water trap does in a flush model: it stops sewer gas without using a drop of water. Because there is no rinse, waterless models depend entirely on routine cleaning to stay fresh.
The practical result is two very different fixtures that solve the same problem. One spends water to move waste and hold a seal. The other spends a consumable cartridge instead. A flush model has more moving parts, since the valve and its sensor can fail. A waterless model has fewer parts but leans harder on a cleaning routine. Knowing how each one holds back odor helps explain why their upkeep looks so different.
How much water does a waterless or low-flow urinal save?
The savings are large, which is the main reason buildings switch. The current federal standard for commercial urinals is 1.0 gallon per flush (gpf), and EPA notes that "some older urinals use as much as five times that amount." A WaterSense labeled flushing urinal uses 0.5 gpf or less. A waterless urinal uses zero.
EPA WaterSense puts the per-fixture savings plainly: "Replacing just one older, inefficient urinal that uses 1.5 gpf with a WaterSense labeled model could save a facility more than 4,600 gallons of water per year." Scale that across a busy building and the numbers grow fast. EPA estimates that "a typical office building could reduce its water use from old, inefficient urinals by 26,000 gallons per year or more."
EPA also notes that the upgrade does not cost you flushing power. Replacing old fixtures with WaterSense labeled urinals "can save between 0.5 and 4.5 gallons per flush, without sacrificing performance." So the water savings do not come at the price of a weak or clogged flush.
For a high-traffic restroom in an office, school, stadium, or restaurant, those gallons add up on the water bill every month. A men's room with a few urinals and steady foot traffic can run through a lot of water a day on flushing alone. In Phoenix, where water conservation is a year-round priority and supply is closely managed, cutting fixture water use is both a cost decision and a responsible one. A single low-flow or waterless urinal can take thousands of gallons off a building's annual use, and a full restroom retrofit multiplies that.
What is the maintenance tradeoff between them?
Neither type is maintenance-free. They just need different work on different schedules, and that tradeoff often decides the choice.
A waterless urinal shifts upkeep to a cartridge and sealant routine. The cartridge or its sealant has to be replaced on the manufacturer's schedule, and the drain line needs periodic flushing to clear the buildup that water no longer rinses away. Skip that schedule and you get odor and slow drainage. Done right, the routine is simple, but it is a recurring cost in cartridges and staff time, and it has to actually happen.
A flush urinal moves the work to the valve. A flushometer can stick open and run all day, run weak, or drip, and the diaphragm or piston inside wears out over time. Hard water makes this worse, since scale and grit can clog the small bypass that controls the flush. Keeping the valve healthy means periodic rebuild kits and matching replacement parts to the fixture's flush rate. Sloan, a major flushometer maker, sells diaphragm and rebuild parts matched to each valve, so a running or weak flushometer is usually a repair rather than a replacement. For the full diagnosis of a valve that will not shut off, see our guide on a flushometer or Sloan valve that keeps running.
| Factor | Flush urinal | Waterless urinal |
|---|---|---|
| Water use | 1.0 gpf federal max; 0.5 gpf or less for WaterSense | None |
| Odor seal | Water-filled trap, refilled each flush | Floating liquid sealant in a cartridge |
| Main upkeep | Flushometer valve rebuilds and part replacement | Cartridge/sealant changes plus drain-line flushing |
| Recurring cost | Repair parts, water bill | Cartridges and sealant |
| Risk if neglected | Running valve wastes water; weak flush | Odor and slow drainage |
The honest summary: a flush urinal costs water and valve repairs, while a waterless urinal trades that water away for a strict cartridge-and-cleaning discipline. Both belong in a written commercial plumbing preventive maintenance plan so the upkeep is scheduled, not reactive.
Are waterless urinals allowed by code, and which fits my building?
Most waterless urinals that use a replaceable sealed cartridge are accepted under U.S. plumbing codes, because the cartridge provides the trap seal that the International Plumbing Code requires to keep sewer gas out of the room. The catch is the design. Some waterless models use a self-sealing mechanical trap instead of a liquid cartridge, and that style is currently not allowed under U.S. codes. Before specifying a waterless fixture, confirm the model is the cartridge type and that the local jurisdiction accepts it.
Accessibility rules apply to both types. Under the 2010 ADA Standards, where urinals are provided, at least one must have a rim no higher than 17 inches above the floor, and the flush controls or any operable parts must work with one hand without tight grasping or twisting. A waterless model has no flush control to worry about, but the rim height still applies.
Which design fits depends on the building. Waterless tends to win in high-traffic, water-conscious settings where staff can commit to the cartridge schedule, such as stadiums, schools, and large offices. Low-flow flush urinals fit buildings that want big water savings without changing cleaning habits, or where users expect a visible rinse. Restrooms with very low use can favor flush models, since the periodic flush keeps the drain line wet and clear. A building owner weighing the switch should look at restroom traffic, who will handle upkeep, and the local code before deciding.
For Phoenix commercial properties, the water savings of either a WaterSense flush urinal or a waterless model are real and recur every year. If you want help choosing fixtures, sizing the savings for your building, or servicing existing urinals, HQ Plumbing & Air handles commercial restroom plumbing across metro Phoenix.