Greywater System Sizing


Calculate the Surge Requirement

Use the chart below to select the Flotender Greywater System which matches the surge requirement of the combined greywater fixtures which will be connected to the system. Refer to the chart to the right for average surge required for common greywater fixtures.

What is Surge?
Surge is the amount of greywater flowing into the system simultaneously.

Looking for a Timed System?
The Flotender System can plugged into a standard outdoor timer to irrigate on a timed schedule.  


install grey water system filter





If all of the greywater fixtures may be used at once:

The building has 6 showers, 1 bathtub, 8 sinks and 1 washing machine connected to the Flotender Greywater Filter.

Showers: 25 gallons x 6 showers = 150 gallons
Bathtub: 50 gallons x 1 = 50 gallons
Sinks: .25 gallons x 8 = 2 gallons
Washing Machine: 25 gallons x 1 = 25 gallons

Totals: 150 + 50 + 2 + 25 = 227 gallons of total surge capacity required.


If only some of the greywater fixtures will be used at once:

Keep in mind that the 227 gallon requirement is taking into account that all of the greywater fixtures may be used at once. If the greywater emitting fixtures will not be used at the same time the amount of surge capacity can be reduced:

Morning: 2 showers & 3 sinks will be used simultaneously requiring 50.75 gallons of surge capacity
Mid-day: 1 washing machine, and 4 sinks will be used simultaneously requiring 26 gallons of surge capacity
Evening: 1 bathtub, 3 showers and 6 sinks will be used simultaneously requiring 126.5 gallons of surge capacity

According to the above estimates, the maximum greywater flow at any one time would be 126.5 gallons, therefore a system which provides 126.5 gallons of surge capacity is required (such as the GL-155-2SP which provides up to 155 gallons of surge capacity)



What happens if the building's greywater output exceeds the surge capacity?
If the building's greywater output exceeds the Flotender's built-in surge capacity, the excess greywater will be routed out through the overflow port and back to the sewer line or to a designated drain sump in the landscape.

Looking to store greywater?

Visit System Types to learn how to use Flotender in a Delayed Distribution Greywater Storage System >


If you have any questions about system sizing or if you would like us to review your project for proper product specification,
give please contact us.

Note: The Flotender Greywater Filter in an Instant Distribution Setup is designed to handle greywater surge only and does not store greywater. Once greywater enters the system it is immediately pumped out for distribution in the landscape. If greywater storage is desired, it must be stored "upstream" from the greywater filter. Learn More >