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Understanding How Wells and Groundwater Systems Work for Well Water Treatment
What is Groundwater?
Groundwater is water that soaks into the soil from rain or other precipitation and moves downward to fill cracks and other openings in beds of rocks and sand. It’s a renewable resource, although renewal rates vary greatly according to environmental conditions. Here in California, we recently experienced a serious drought, but thankfully, we had ample rain this past winter.
It is also an abundant natural resource. Of all the fresh water in the world (excluding polar ice caps), 95 percent is groundwater. Surface water (lakes and rivers) only makes up three percent of our fresh water.
Scientists estimate U.S. groundwater reserves to be at least 33,000 trillion gallons, equal to the amount discharged into the Gulf of Mexico by the Mississippi River in the past 200 years. These reserves are a critical part of wells and groundwater systems that supply homes, farms, and communities across the country.
Groundwater is naturally filtered by the earth that holds it. It can, however, be contaminated by pollutants that come into contact with the Earth’s surface. Care should be taken at the household, local, national, and global levels to protect wells and groundwater systems from pollution and overuse.
The Making of Groundwater Flow
Water from rain and snow follows three main paths:
- Some water evaporates from the Earth’s surface into the air or is breathed out by vegetation and returns to the Earth’s atmosphere. Some water runs off into streams, lakes, or oceans.
- Some filter into the ground. There, it can flow to the surface as springs, move into surface water, or recharge groundwater deeper in the earth.
- Groundwater can move into large underground natural storage areas known as aquifers and/or artesian wells.
These processes are part of the hydrologic cycle, which describes the continuous movement of water on, above, and below the Earth’s surface.
As groundwater moves through the ground, it dissolves some of the minerals it comes in contact with, such as limestone and iron. Those dissolved minerals give groundwater its chemical character or quality.
Much bottled water comes from groundwater reserves.
Groundwater Flow and Quality
Understanding groundwater systems begins with how water moves underground and what affects its quality. Groundwater flow describes water traveling through the saturated zone beneath the Earth’s surface, driven mainly by gravity and hydraulic gradients—differences in water pressure within the aquifer. Flow rates vary based on geology permeability, hydraulic gradient, and water extraction volume.
Groundwater quality depends on the aquifer’s geological makeup, soil types, and human activities like agriculture, urbanization, and industry. Contaminants such as nitrates, pesticides, and heavy metals can enter through surface water, soil, and rock, threatening water quality.
Confined aquifers, trapped between impermeable rock or clay layers, are less vulnerable to surface contamination but can be affected by pollutants seeping through cracks or poor well construction. Unconfined aquifers, directly recharged by surface water, are more exposed to contamination from agricultural runoff, septic tanks, and surface activities.
Regular testing and monitoring are vital to protect groundwater resources and ensure safe water supplies for well owners.
Groundwater and Private Drinking Water Supply Wells
Private water wells tapping groundwater resources can frequently provide the highest quality water available to homeowners and businesses. Deep-drilled wells recharge themselves and can provide a constant, steady supply of water that is not easily impacted by dry weather conditions.
The proper management of groundwater basins is crucial to ensure a sustainable and high-quality water supply for private wells.
According to an independent market survey sponsored by the National Ground Water Association (NGWA), 78 percent of private water well owners prefer receiving their drinking water from their wells. Eighty-eight percent of those surveyed said private wells were their least expensive drinking water option.
Private water wells also allow homeowners to control their water quality more. They can store the water and have it available for emergencies.
What exactly is a drilled well?
A drilled well is a borehole lined with casing in its upper portion. The casing prevents collapse and helps block surface or subsurface contaminants, especially when sealed with grout or a drive shoe.
Inside the casing, a submersible well pump and pipe carry water to the surface. Water enters through the intake at the bottom of the well, which may be an open hole in rock or screened and gravel-packed, depending on geology.
The water table marks the point where the ground becomes fully saturated. After drilling, the well must be developed to remove debris and improve flow. A yield test—lasting at least one hour—measures water production.
Disinfection is a key step to kill any bacteria introduced during drilling. The well is then capped to protect it until it connects to the home. Well caps should include an air vent.
Most homes use submersible pumps to maintain steady pressure, controlled by a pressure switch. Jet pumps typically sit above ground and draw water from shallow wells under 30 feet, which makes them more prone to contamination.
In many areas, local agencies don’t regulate private wells, so homeowners are responsible for maintaining water safety and quality.
Basic Types of Wells
There are several basic types of wells, each with unique features suited for different water supply needs:
- Dug Wells are hand-excavated and typically 10 to 30 feet deep. Lined with stone, brick, or concrete, they serve individual homes or small farms. Their shallow depth makes them more vulnerable to surface contamination.
- Driven Wells are built by driving small-diameter pipes into soft ground like sand or gravel. Usually 30 to 50 feet deep, they’re easy to install and often used for irrigation or non-potable water. Like dug wells, they’re more prone to contamination.
- Drilled Wells are the most common and can reach depths over 1,000 feet. Created using drilling rigs, they access deep aquifers and are ideal for residential, municipal, and industrial water needs. Their depth makes them less likely to become contaminated.
- Artesian Wells access pressurized aquifers, often flowing naturally to the surface. These wells are a reliable source of clean drinking water and are ideal where suitable geology exists.
Choosing the right type of well depends on your location, water needs, and risk of contamination. Understanding these differences can help you select the best option for a safe, long-term water supply.
Potential Sources of Private Well Contamination
Before you can treat well water, you might want to have your water tested and look for signs of contamination by testing the water.
If you live in a rural area with your own well, the well often has a number of potential sources of groundwater contamination near the wellhead:
- Septic system
- Improper waste disposal – paints, lubricants, dead animals, cleaning products, etc.
- Pesticide and fertilizer storage, mixing, and loading
- Livestock pens, corrals, manure stockpiles, and lagoons
- Leaky silos or underground silage pits
- Lawn and garden chemicals
- Abandoned or poorly sealed wells
- Old waste dumps
- Underground storage tanks
- Equipment and vehicle cleanup and maintenance
- Fuel storage, old underground fuel tank
- Hydro-fracking involves injecting steam and chemicals into the ground to extract petroleum from oil shale formations. Fracking operations can contaminate some local wells, although typically, they occur at far deeper depths than the groundwater layer and have little overall effect (as far as we know at this time).
Older wells in shallow aquifers are more likely to be contaminated. The soil and geologic material that overlies the aquifer greatly influences the relationship between surface activities and groundwater quality.
Deeper wells often pass through more restrictive or impermeable layers that decrease the rate at which surface water reaches the aquifer.
You should talk to the driller who installed their well about the hydrogeology of their site and ask for a copy of the well log (a record of well construction and geologic formations encountered).
While all wells need protection, it is especially important to observe good management in the vicinity of a shallow or vulnerable well.
What Can You Do To Prevent or Correct Contamination?
State regulations encourage good well location by requiring a minimum separation of 100 feet between new wells and contamination sources. Septic tanks and sewer lines must be at least 50 feet away, with some counties enforcing greater distances.
Contamination from faulty well caps or missing grout often leads to coliform bacteria in well water. The first step in managing a private well is annual testing for total coliform bacteria, available through local certified labs or home test kits.
If coliform bacteria are detected, installing a sanitary well cap can help, especially with low bacteria levels. You may also sanitize your well using a 100 ppm bleach solution (1 cup household bleach per 31.2 gallons of water) during maintenance or repairs. Adjust chlorine levels based on well depth, and use a high-level chlorine test kit to avoid over- or under-dosing, which can harm pumps or be ineffective.
Resources:
- California State Water Resources Control Board – Residential Water Treatment Devices: This page discusses various water treatment devices and their effectiveness in treating different contaminants in well water. California State Water Resources Control Board
- Rhode Island Department of Health – Filtration and Treatment of Private Well Water: Here, you can find information on how to choose a water treatment system for your private well, including contact information for further assistance. RI Department of Health – Well Water Treatment
- State Hygienic Laboratory – Well Water Quality and Home Treatment Systems: This PDF document offers insights into well-water home treatment systems, including traditional methods and modern technologies. Well Water Quality and Home Treatment Systems
Frequently Asked Questions (FAQs)
1. What is groundwater, and how does it form?
Groundwater forms when rain and snow seep into the soil, moving down to fill cracks in rock and sand layers. It’s a major source of fresh water in the U.S.
2. How does a private water well work?
Private wells tap into groundwater sources. Most use a submersible pump and casing to draw and protect the water, providing a constant supply to the home.
3. What can contaminate a private well?
Contamination can come from nearby septic systems, agricultural runoff, fuel storage, or improper waste disposal near the wellhead.
4. What is the difference between jet and submersible pumps?
Jet pumps sit above ground and are used for shallow wells. Submersible pumps, installed in deeper wells, push water to the surface.
5. How can I protect the water quality of my well?
Test your water annually for bacteria, install a sanitary well cap, maintain proper setbacks from contaminants, and disinfect your well after any system work.
