EPA estimates that about 40,000forty thousand SSO events occur in the [[United States]] each year.<ref>U.S. Environmental Protection Agency (EPA). Washington, DC. [http://cfpub.epa.gov/npdes/home.cfm?program_id=4 "Sanitary Sewer Overflows and Peak Flows"], Updated February 2012.</ref> The AgencyEPA estimated that upgrading every municipal treatment and collection system to reduce the frequency of overflow events to no more than once every five years would cost about $88 billion dollars as of 2004.<ref name="EPA-RTC">
EPA. [http://cfpub.epa.gov/npdes/cso/cpolicy_report2004.cfm "Report to Congress: Impacts and Control of CSOs and SSOs"], Executive Summary. August 2004. Document No. EPA-833-R-04-001.</ref> This cost would be in addition to approximately ten$10 billion dollars already invested. Although the volume of untreated sewage discharged to the environment is less than 0.01% of all treated sewage in the United States, the total volume amounts to several billion U.S. gallons per annum and accounts for thousands of cases of gastrointestinal illness each year.<ref name="EPA-RTC" />{{rp|Ch. 6}} Advanced European countries and Japan have similar or somewhat larger percentages of SSO events.<ref>{{cite web|url=http://septiczone.com/global-sso-events |title=A Worldwide View Of Sanitary Sewer Overflow |accessdate=19 July 2009}}</ref>{{Failed verification|date=June 2015}}
