Stormwater Management and how Equivalent Residential Units (ERU) are calculated

The information contained herein is provided by the City of Henderson Water Utility as a general reference to those customers who have questions or are interested in a detailed explanation of how the fees are calculated under the Stormwater Management Plan adopted as Ordinance 01-98, by the City Board of Commissioners on January 27, 1998.

The following explains the method of determination, assessment and billing of stormwater fees to customers within the City of Henderson Water Utility (HWU) water service area which includes all HWU customers outside the city limits of Henderson.

Equivalent Residential Units (ERU) means the basic unit for the computation of storm water service fees. All single family dwelling units are considered one (1) ERU regardless of the actual lot or structure size and are considered to have an average impervious area of three-thousand (3,000) square feet consisting of an average roof area of 2,500 square feet and an average impervious paved surface area of 500 square feet.

Equivalent Residential Units greater than one (1) are expressed in whole numbers without fractional values. Impervious area determinations are rounded to the nearest whole number.

Impervious Areas mean the horizontal-projected plain area of roof and paved areas of all permanently constructed roofs of houses, garages, mobile homes, businesses, industries, paved driveways, patios and parking lots, but does not include non-permanent structures such as temporary buildings and tents. Also excluded are impervious areas of stored materials and equipment, swimming pools, ponds and lakes; and storm water retention and detention basins. Gravel or rock roads and gravel or rock parking areas are not considered as impervious areas.

Single-family property includes all single-family separate individual housing units. Attached or multiple single family units served by individual water meters to each unit are also considered under this category. This category includes mobile homes served by individual water meters. All other residential development are classified as "multi-family.

Multi-family residential properties include all duplex, condominium, mobile home park, apartment and other properties containing more than one (1) dwelling unit unless each dwelling unit is served by an individual water meter. Also included are residential unit(s) in a multi-occupancy building of a predominantly non-residential nature, such as a multi-story building with retail, office and residential uses. Common areas associated with such properties are included in the charge to the "multi-family" units on said properties.

Non-residential property includes all property zoned or used for commercial, industrial, retail, agricultural, governmental, or other non-residential purposes and includes all developed real property in the HWU water service area not classified as single-family or multi-family as defined in this section.

All customers with developed residential or commercial property with an Active Water Service Account within the HWU water service area, except for customers of the HWU South Water System and wholesale customers, pay a monthly stormwater fee based, in general, on their contribution to storm water runoff, which is based on the ERU's of the properties multiplied by the monthly rate per ERU (currently $2.00 per ERU).

The stormwater ERUs for all residential properties are as follows:

Single family home units = 1 ERU/home unit
Duplex units = 1 ERU/dwelling unit
Condominium units = 1 ERU/dwelling unit
Apartments = 0.6 ERU/dwelling unit
Mobile Homes (single family) = 1 ERU/mobile home
Mobile Homes (multi-family) = 0.6 ERU/lot

Mobile Homes in the single family category are those served by individual water meters. Mobile Homes in the multi-family category Are those served by a common water meter.

The ERUs for all non-residential/commercial property are calculated based on the total impervious roof and paved surface areas as follows:

The total roof area is divided by 3,000 to determine the equivalent number of Roof ERU's (RERU). The total impervious area of paved surface area is divided by 3,000 to determine the equivalent number of Paved ERUs (PERU). The total number of ERUs for the property is then the number of RERUs plus one-half (1/2) of the number of PERUs, the sum of which is rounded to the nearest whole number.

In the event a property does not have an Active Water Service Account but is determined to have impervious area equivalent or greater than two (2) ERU's, a new stormwater only account is developed and that property is billed for the stormwater fees.

For new developments and/or as other special circumstances may require, all non-residential/commercial properties for which the actual impervious areas have not been determined pay a minimum monthly fee based on one (1) ERU, until the actual or correct impervious areas are determined.

We hope this adequately addresses any questions you had concerning the stormwater fees; however, if after reading this information thoroughly you still have questions, please contact Henderson Water Utility at (270) 826-2824.