Siloam Springs, Arkansas

===Utilities===
[[File:Siloam Springs WWTP 001.jpg|thumb|right|[[Sewage treatment#Primary treatment|Primary clarifier]] (foreground) and [[Aerated lagoon#Suspension mixed lagoons|aeration basins]] (background) at Siloam Springs Wastewater Treatment Plant]]
The city's primary water source is the [[Illinois River (Oklahoma)|Illinois River]], although some water is purchased from Benton - Washington Regional Public Water Authority, whose source is [[Beaver Lake (Arkansas)|Beaver Lake]].<ref>{{ cite web |publisher= Siloam Springs Water Department |year= 2012 |title= Annual Drinking Water Quality Report }}</ref> The water is treated with [[chlorine]], and the by-products of this chlorination process are kept compliant with the [[Arkansas Department of Health]] standards. [[Fluoride]] is added to supplement the naturally occurring amount present prior to treatment.

Wastewater is treated at the Siloam Springs Wastewater Treatment Plant (SSWWTP). Since effluent is discharged into a tributary of the Illinois, the plant's effluent is required to meet the treatment standards of both Arkansas and Oklahoma. The [[phosphorus]] load of the Illinois has been subject of controversy in the area, even reaching the [[United States Supreme Court]] in 1992. The [[Environmental Protection Agency]] (EPA) has classified the Illinois as Section 303(d) of the [[Clean Water Act]], listing it as an "impaired and threatened water" due to the high phosphorus loads.<ref>{{ cite web |title= Illinois River Watershed |date= May 22, 2013 |publisher= Environmental Protection Agency |url= http://www.epa.gov/region6/water/npdes/illinoisriverwatershed/ |access-date= July 21, 2013 }}</ref> As a result of the applicable strict phosphorus effluent regulations, SSWWTP upgraded its system in 2011. The upgrades also increased capacity 25% to 5.5 million gallons per day (MGD) (14,474 liters per hour).<ref>{{ cite web |title= Arkansas wastewater treatment plant pilots path to fledgling technology |first= Jon |last= Hetzel |date= February 2007 |url= http://www.apwa.net/Resources/Reporter/Articles/2007/2/Arkansas-wastewater-treatment-plant-pilots-path-to-fledgling-technology |publisher= APWA |access-date= July 20, 2013 }}</ref> Although presently a traditional [[Sewage treatment#Biological nutrient removal|biological nutrient removal]] (BNR) plant capable of meeting the interim phosphorus limit, pilot tests have proven a [[Sewage treatment#Biological nutrient removal|chemical nutrient removal]] (CNR) and [[Membrane bioreactor|membrane biological reactor]] combination to be effective well below the possible future permit limit. However, due to the high cost, these phases have been delayed. Currently, a 3-year study is being conducted to determine the background phosphorus level in the Illinois. The future effluent limits will likely be written following the conclusion of the study. An EPA [[total maximum daily load]] (TMDL) study in the watershed is also ongoing.<ref>{{ cite web |title= Oklahoma Attorney General's Office, Arkansas AG Sign Illinois River Agreement |date= February 20, 2013 |url= http://www.oag.state.ok.us/oagweb.nsf/srch/44A6921A1E42543E86257B180068307E?OpenDocument |publisher= State of Oklahoma Attorney General's Office |access-date= December 10, 2013 }}</ref>