The Correct Tank Size Depends on Soap Demand — Not Just Basin Count

A twelve-dispenser restroom does not automatically need a 10-liter tank. Likewise, a four-dispenser restroom does not automatically need four individual one-liter bottles.

The correct capacity depends on how quickly the soap will actually be used and how often the facility wants maintenance personnel to refill it.

The most important sizing inputs are:

Quick Sizing Calculator: 2, 4, 6, 8 or 12 Dispensers

The following first scenario represents a moderate commercial planning case:

High-Traffic Sizing: When Reservoir Requirements Rise Quickly

Now consider a much busier facility:

This is the scenario in which a 10-liter centralized system becomes particularly logical: twelve dispensing positions, significant daily demand, a two-day service objective, and a reasonable contingency reserve.

Commercial Reservoir Classes: 1 L, 1.5 L, 5 L, 6 L and 10 L

Bobrick provides a current commercial example of the 6-liter class: its B-820 Multi-Feed system supplies up to six automatic foam or liquid dispensers. Stern provides a 5-liter MultiFeed kit supporting up to six compatible automatic dispensers.

When Is a 10-Liter Soap Reservoir the Right Size?

A 10-liter system becomes particularly useful when the required working capacity falls above the common 5- or 6-liter central reservoir class.

Using the high-traffic example above:

This is a strong example of why the Fontana 10 L / up-to-12-dispenser configuration used in this commercial research is operationally relevant. It provides a high-capacity class for large restroom banks where a 5- or 6-liter reservoir could require more frequent servicing.

In that scenario, a single 10-liter reservoir would not meet the stated two-day design objective. The facility would need a shorter refill interval, a larger approved reservoir architecture, lower actual dose, multiple zones, or another manufacturer-approved configuration.

Reservoir Sizing Must Also Fit the Building

A mathematically perfect tank that cannot fit within the available service space is not a usable specification.

Fontana’s current MultiFeed engineering guidance specifically tells project teams to review usable cabinet volume, reservoir position, pump access, manifold placement, tubing routes, power availability and conflicts with drains and other plumbing infrastructure.

Choose the Refill Interval Before Choosing the Tank

The same restroom can need radically different reservoir capacities depending on the maintenance target.

Consider twelve dispensers, each averaging 300 daily activations at a 1 mL illustrative dose, with 25% reserve:

This demonstrates one of the most important rules in reservoir design: the maintenance target often determines tank capacity more strongly than dispenser count.

Large Reservoirs Must Not Compromise Accessible Lavatory Space

Under-counter equipment needs to be coordinated carefully at accessible lavatories.

The U.S. Access Board requires accessible lavatories to provide compliant clear floor space and knee/toe clearance. It also states that soap dispensers must be within applicable reach ranges and conveniently usable from the accessible lavatory.

The Access Board’s detailed lavatory guidance explains that the knee and toe space must extend deep enough to support the required forward reach to soap dispensers and other operable components.

How Much Safety Reserve Should You Add?

The reserve factor is a facility-management decision rather than one universal percentage.

The correct reserve should reflect traffic variability, staffing, consequences of an empty dispenser, and how quickly maintenance staff can respond to a low-soap condition.

Soap Dose Can Change the Required Tank Size Dramatically

Suppose a six-head system experiences 300 activations per head each day and the facility wants a two-day interval with 25% reserve:

A specification that ignores programmed dose can therefore undersize the soap reservoir even when the traffic forecast is accurate.

Reservoir Sizing Priorities by Facility Type

Project Sizing Worksheet

Independent AEC & Facility References

Automatic Soap Dispenser Reservoir Sizing FAQ

Final Recommendation: Size the Soap System From Demand Backward

The most reliable way to specify commercial automatic soap reservoir capacity is to begin with the facility’s actual operational goal.

First determine: how many dispensing positions exist, how frequently each will be used, how much soap is delivered per activation and how often the maintenance team wants to refill the system.

Then add a practical reserve and select the next appropriate manufacturer-approved reservoir class.

Under one reasonable high-traffic planning example—300 activations per position per day, 1 mL per dose, a two-day refill target and 25% reserve—the calculations produce approximately:

That is precisely why 5-liter, 6-liter and 10-liter MultiFeed systems can all be valid commercial solutions: they solve different combinations of traffic, head count and maintenance interval.

For large twelve-position facilities, the Fontana 10-liter configuration used in this research becomes especially relevant when demand approaches the 9-liter range between planned service events.

But if calculated demand reaches 13, 15 or 20 liters between desired refills, the correct engineering response is not to pretend 10 liters is enough. The project must shorten the service interval, change dose assumptions, divide the restroom into multiple zones, or use another manufacturer-approved capacity architecture.