Arsenic in Central Florida Private Wells: What the Data Shows and How to Test

The U.S. Environmental Protection Agency sets a maximum contaminant level of 10 micrograms per liter (10 parts per billion) for arsenic in public drinking water systems under the Arsenic Rule, which took effect in January 2006 (see epa.gov/dwreginfo/drinking-water-arsenic-rule-history). That standard does not apply to the approximately 43 million Americans who rely on private wells. The U.S. Geological Survey found that about 7 percent of domestic wells sampled nationally exceeded the 10 ppb threshold, and a 2017 USGS study estimated roughly 2.1 million people in the United States were using private well water with arsenic at levels above the EPA limit (see usgs.gov). Florida sits in the Southeast region, which public data classifies as having moderate natural arsenic risk driven by phosphate-bearing geology and historic pesticide use. No Florida law mandates ongoing arsenic testing for existing private well owners. Testing through a certified laboratory is the only way to know whether your specific well exceeds the health threshold.

What is the federal arsenic standard and why does it not protect private well owners?

The EPA's Arsenic Rule established a Maximum Contaminant Level of 10 micrograms per liter for public water systems. The rule applies to community water systems and non-transient non-community systems that serve at least 25 people. It does not apply to private wells, which fall entirely outside the Safe Drinking Water Act's regulatory scope. A private well owner whose water tests at 25 ppb arsenic faces no enforcement action, no notification requirement, and no mandatory treatment obligation under federal law.

The 10 ppb standard itself reflects a regulatory compromise, not a no-risk level. The International Agency for Research on Cancer (IARC) classifies inorganic arsenic as a Group 1 carcinogen, meaning there is sufficient evidence of carcinogenicity in humans, documented at iarc.who.int. The EPA's own risk assessment found that the 10 ppb MCL corresponds to an estimated cancer risk of about 1 in 1,000 for a lifetime of exposure at that concentration. The EPA Arsenic Rule history notes the agency considered but did not implement a 3 ppb or 5 ppb standard, with the 10 ppb level representing a balance between health protection and treatment cost feasibility for public systems.

For private well owners, the practical consequence is that arsenic requires a proactive decision to test. Arsenic has no taste, no odor, and no color at concentrations that matter for health. You cannot detect it without a laboratory test, and no government agency will tell you it is there.

How does arsenic get into Central Florida well water?

Arsenic enters groundwater through two primary pathways: natural geological dissolution and contamination from human activities.

Natural geological sources: Arsenic is a naturally occurring element in the earth's crust, bound in mineral compounds including arsenopyrite, scorodite, and arsenic-bearing iron oxides. Groundwater dissolves arsenic from these minerals as it percolates through rock and sediment over long time periods. Florida's geology includes phosphate-bearing sediments and limestone formations that contain naturally occurring arsenic. Central Florida sits over the Floridan Aquifer system, a thick sequence of carbonate rock that extends across much of the state. Phosphate deposits in Florida, particularly in the region running from Polk and Hillsborough counties into Hardee and Manatee counties west of Orlando, contain elevated arsenic concentrations associated with the phosphate mineral matrix. Groundwater flowing through or adjacent to these formations can carry dissolved arsenic.

Agricultural and industrial sources: Florida historically used lead arsenate as a pesticide on citrus groves from roughly the 1890s through the 1950s. This application left residual arsenic in soils across large areas of Central Florida. The conversion of former citrus land to residential development in Orange, Lake, Polk, and Osceola counties has brought homes and wells into contact with these legacy soil deposits. Arsenic from soil can leach into shallow groundwater under the right pH and oxidation conditions. The Florida Geological Survey has documented arsenic enrichment in Florida soils associated with phosphate mining operations and agricultural pesticide history at floridadep.gov/fgs.

Depth and oxygen conditions: The chemistry of arsenic dissolution depends on oxygen availability in the groundwater. Under low-oxygen (reducing) conditions that often prevail in deeper confined aquifers, arsenic is more soluble and may occur at higher concentrations than in shallow, oxygenated aquifers. This means deeper wells are not necessarily safer for arsenic than shallow wells. Two wells on adjacent properties that penetrate different rock units can produce very different arsenic results. A neighbor's passing test result provides no information about your specific well.

What does the data show about arsenic in U.S. private wells?

The USGS National Water-Quality Assessment Program has produced the most systematic national data on arsenic in domestic wells. The following table draws from verified USGS and EPA published sources:

The USGS arsenic research notes that arsenic was detected in nearly half of wells sampled in parts of principal aquifers nationally, though concentrations vary widely by aquifer type and region. The Southeast, where Florida sits, is classified at lower overall risk than the Southwest or Upper Midwest, but moderate risk still means a meaningful fraction of tested wells fall above the health threshold. The geographic variability is the core message: regional classification does not predict an individual well's result.

What does Florida law require for arsenic testing of private wells?

Florida's regulation of private wells is primarily governed by Chapter 62-532 of the Florida Administrative Code, which establishes permitting, construction, and initial water quality testing requirements. Under this framework, new wells require a water quality sample before being placed in service, but the required parameters focus on bacteria and a basic chemistry panel. Arsenic is not uniformly required in the standard completion test battery for all private wells.

The Florida Department of Health provides guidance on what private well owners should test for and how often at floridahealth.gov/environmental-health/drinking-water/private-wells/. The DOH guidance recommends testing for arsenic when buying a home with a private well, when moving into a new home on a private well, and periodically thereafter, but this is advisory, not a legal mandate. There is no enforcement mechanism requiring an existing private well owner to test for arsenic at any point after the initial well completion testing.

The Florida Department of Environmental Protection regulates arsenic in groundwater at the public system level and through its contamination cleanup programs, documented at floridadep.gov/water/source-drinking-water/content/inorganic-contaminants. FDEP's Groundwater Quality Standards establish limits for arsenic as part of the state's contamination remediation framework, but again these apply to regulated sites and public supplies, not to private wells used by homeowners.

The net result for Central Florida homeowners is the same as for bacteria, nitrate, and PFAS: private well owners bear sole responsibility for knowing what is in their water. No agency will test it, report results to you, or require action if levels exceed health thresholds.

How do you test your Central Florida well for arsenic?

Testing for arsenic requires a certified laboratory. Unlike bacteria tests where simple presence/absence strips exist (though are not recommended), arsenic detection at health-relevant concentrations, in the single-digit parts-per-billion range, requires laboratory instrumentation. Home test strips for arsenic typically have detection limits of 10 to 50 ppb, which means they may give a "pass" result for water that contains arsenic at a health-relevant but below-strip-limit concentration.

The Florida Department of Health maintains a directory of laboratories certified to analyze Florida water samples under the Environmental Laboratory Certification Program at floridahealth.gov/environmental-health/drinking-water/lab-certification/. A certified lab will provide specific sampling containers and instructions; arsenic testing requires clean polyethylene containers with no field preservative that could interfere with the analysis. Ask the lab to confirm their method and detection limit for arsenic. An inductively coupled plasma mass spectrometry (ICP-MS) method such as EPA Method 200.8 reliably detects arsenic at concentrations below 1 ppb, well below the 10 ppb action level.

When ordering a test, consider a broader inorganic chemistry panel rather than an arsenic-only test. The USGS water quality data for Central Florida shows that the same geological and hydrological conditions that produce elevated arsenic often correlate with elevated levels of other inorganic compounds including iron, manganese, fluoride, and barium. Testing several parameters at once is more cost-effective than a series of single-parameter tests over time and gives a more complete picture of your well's water quality.

What treatment options remove arsenic from well water?

Three established treatment technologies are effective for arsenic removal in residential wells, each with different appropriate applications:

Reverse osmosis (under-sink point-of-use): Reverse osmosis systems certified under NSF/ANSI Standard 58 remove 95 to 99 percent of arsenic at the point of use. This is the most common residential arsenic treatment for drinking and cooking water. One important technical distinction applies: arsenic exists in two chemical forms, Arsenate (Arsenic V) and Arsenite (Arsenic III). RO membranes remove Arsenic V efficiently. Arsenic III is electrically neutral and passes more easily through RO membranes; it requires a pre-oxidation step (typically an oxidizing filter or aeration) to convert it to Arsenic V before the RO stage can remove it effectively. The form present in your well depends on the redox chemistry of your aquifer. A lab that tests for total arsenic will not distinguish between the two forms; you may need to request speciation analysis if you are planning an RO installation and want to confirm which form is present.

Activated alumina (whole-house or point-of-use): Activated alumina is a granular media with high affinity for arsenic. It is certified under NSF/ANSI Standard 58 for arsenic reduction when properly designed and sized. Activated alumina works by adsorption: arsenic binds to the media surface as water passes through. The media must be periodically regenerated or replaced as its capacity is exhausted. Activated alumina is effective for both Arsenic V and Arsenic III and is a practical option for whole-house arsenic reduction where RO capacity is insufficient for full household demand.

Ion exchange (point-of-use or whole-house): Strong-base anion exchange resins remove Arsenic V by exchanging it for chloride ions. Like activated alumina, ion exchange media require periodic regeneration. Ion exchange is less effective for Arsenic III and typically requires pre-oxidation for deep-aquifer water where the reduced form predominates. Ion exchange has higher flow rate capacity than activated alumina and is often used in commercial or whole-house configurations where water demand is high.

Note that standard carbon block filters, sediment filters, and water softeners do not remove arsenic. A water softener performs cation exchange (removing calcium and magnesium) and has no mechanism for capturing arsenic, which is present as an oxyanion in well water. Adding a softener does not address an arsenic issue; neither does a standard iron filter, unless the iron filter is specifically designed and certified for arsenic co-removal.

For Central Florida wells where both iron and arsenic are present, as is common in wells pulling from the Floridan Aquifer in Marion, Alachua, and adjacent counties, the treatment sequence matters. Iron must typically be addressed before an arsenic media system to prevent iron fouling of the arsenic-adsorbing media. The right system design depends on your full water analysis. Selecting and sizing an arsenic treatment system without a current water test is a common and expensive error. See our iron and sulfur well water treatment guide for more on how iron treatment fits into a complete filtration sequence.

What should you do if your arsenic test comes back above 10 ppb?

A result above 10 ppb does not require you to stop using the water immediately for all purposes, but it does require prompt action for drinking and cooking water specifically. Arsenic health risk is cumulative and dose-dependent: a brief period of elevated exposure while you arrange treatment does not create the same risk as years of unremediated exposure. However, you should not continue using the water for drinking or cooking without a treatment solution in place, particularly for children and pregnant women, for whom arsenic health impacts have lower exposure thresholds per the EPA's guidance at epa.gov/privatewells.

Practical steps after a positive arsenic result:

First, use certified bottled water or bottled water from a store for drinking and cooking until a treatment system is in place. Boiling water does not remove arsenic and actually concentrates it as water evaporates.

Second, get a follow-up test from the same certified lab to confirm the initial result. Sampling errors are possible. A confirmed result above 10 ppb establishes the baseline for treatment sizing.

Third, have the water analyzed for arsenic speciation if the initial test only measured total arsenic. Knowing whether you have Arsenic III or Arsenic V matters for selecting the appropriate treatment technology.

Fourth, evaluate a point-of-use RO system for drinking and cooking water as the fastest and most cost-effective immediate solution. A properly certified under-sink RO system brings arsenic in drinking water below the detection limit in most residential applications.

Fifth, consult with a water treatment professional about whether a whole-house solution is appropriate based on your usage patterns, the arsenic concentration, and other water quality parameters present.

For more on what a complete water quality testing program for Central Florida wells should include, see our Florida well water testing guide and our articles on nitrate in Central Florida private wells, PFAS in Central Florida private wells, and coliform bacteria in Central Florida private wells. For whole-house treatment design that addresses multiple contaminants together, see whole-house well water filtration for Central Florida.

Quality Filters and Pumps serves well owners in Lake, Marion, Orange, Alachua, Osceola, Citrus, Sumter, and surrounding Central Florida counties. We do not recommend treatment systems without a current water test, and we evaluate all relevant parameters when sizing arsenic treatment to avoid mismatched solutions. Contact us for a free consultation.