Saltwater Intrusion in Well Water: Signs, Testing and What to Do

Saltwater Intrusion in Well Water: The Short Answer

If your coastal well has started to taste salty, the number to watch is chloride, not your taste buds. Chloride can climb well past the level USGS researchers have used to flag possible intrusion before it reaches the level where the EPA expects a salty taste, and it's the marker USGS studies use to track saltwater intrusion: seawater moving into the fresh groundwater a well draws from.

Intrusion usually creeps in slowly, and pumping is often part of the reason. According to the U.S. Geological Survey, groundwater pumping can reduce the flow of fresh water toward the coast and draw saltwater toward the freshwater parts of an aquifer. It has happened to some degree in many coastal aquifers across the country.

If you own a well near the coast, the practical answer comes down to three moves. Get a lab test for chloride and sodium so you have a baseline, then repeat it so you can see whether the numbers are climbing. If they are, look at how the well is pumped first, though anyone in your home on a low-sodium diet shouldn't wait on that to get treated drinking water. And for the water you drink, know that a water softener won't take the salt out. Reverse osmosis or distillation at the kitchen tap is what the University of Maryland Extension recommends for lowering sodium.

How Seawater Gets Into a Fresh Well

Along the coast, fresh groundwater sits on top of seawater. A USGS study of Lopez Island, Washington describes the fresh water as a lens-shaped layer floating on the denser seawater, with its weight holding the salt water down. Between the two is a transition zone where they gradually mix.

Pumping upsets that balance. Pull fresh water out and there's less weight pressing the seawater down, so the transition zone moves up toward the well. The same report says prolonged or large-scale pumping can raise that zone all the way to the well, which may then start drawing in salty water.

Pumping isn't the only driver. USGS also studies sea level rise as a contributor, and it lists leaking saltwater canals, leakage between aquifers and upwelling of saltwater from depth among the other ways salt has reached fresh aquifers. Even under natural conditions, the transition zone shifts slightly as the tide rises and falls and as recharge changes through the seasons.

In extreme cases, USGS notes, intrusion shrinks the fresh water stored in an aquifer and can lead to wells being abandoned. You don't need to be anywhere near that point to care. A rising trend caught early leaves you far more options than salt you discover by taste.

Signs Your Well May Be Affected

Taste is the sign most people notice, and it's a late one. The EPA lists a salty taste as the noticeable effect when chloride goes above its secondary standard of 250 mg/L, or when total dissolved solids pass 500 mg/L. Those are guidelines for taste and appearance, and the EPA doesn't enforce them. Chloride can climb a long way before your coffee tastes off.

Sodium matters sooner for some households. The EPA's sodium advisory recommends that drinking water not exceed 20 mg/L for people on a very low sodium diet of 500 mg a day, and not exceed 30 to 60 mg/L to avoid taste problems for taste-sensitive drinkers. The UMD Extension sodium fact sheet names people with high blood pressure, kidney or heart disease among the groups who should be particularly concerned about sodium. If that's someone in your home, go by a test result, not your taste buds.

Salty doesn't always mean seawater

Before you blame the ocean, rule out the closer suspects. Road deicing salt, home water softeners and agricultural chemicals can all push sodium up in well water, according to UMD Extension. Chloride has its own list of local sources. On Lopez Island, USGS researchers named airborne sea spray in rain, heavy well pumping, septic systems, animal manure and old seawater left in the aquifer as reasons a reading above normal isn't, by itself, proof of intrusion. That's why a trend over time tells you more than any single reading.

After a storm surge

Seawater washing over a wellhead during a hurricane or storm surge is a different problem from slow intrusion through the aquifer. Treat it as a flooded well and work through the steps in our guide to well water after flooding before anyone drinks from it.

How to Test Your Well for Saltwater Intrusion

You'll want real numbers here, so skip the guesswork and ask a state-certified laboratory for three things:

• Chloride. This is the key marker. USGS explains that chloride is a major part of seawater, is chemically stable and moves at about the same rate as the intruding seawater, which is why a rising chloride level is used as an indicator of intrusion.
• Sodium. It's the number that matters for anyone watching their sodium intake, and it's what the EPA advisory levels above refer to.
• Specific conductance or total dissolved solids. Both describe how much is dissolved in the water overall. USGS measured specific conductance alongside chloride in its Lopez Island well sampling.

UMD Extension recommends a state-certified lab for all water testing and suggests calling your local health department for help finding one. It also recommends retesting sodium every three years if the first test comes back high. Whatever schedule you settle on, test at the same time of year each time. The transition zone moves with the seasons, even if only slightly, and matching the season keeps that movement from muddying your trend.

Reading the Numbers

The 100 mg/L figure came from studies in one Washington county, and your local health department may use a different benchmark. Treat it as a reference point, not a verdict. A well that read 20 mg/L for years and now reads 60 is telling you more than a well that has always read 60.

What to Do If Chloride Is Rising

Start with the well itself, because the cheapest fix is often pumping less water, less aggressively. The USGS Lopez Island report lists well practices that help hold seawater back:

• Size pumps for lower pumping rates and keep pumping cycles short.
• If you have more than one well, pump them alternately.
• Use low-volume plumbing fixtures and toilets, and keep outdoor watering to a minimum.
• Reuse or recycle water where you can.
• If you're drilling a new well, don't go deeper below sea level than necessary.

Talk with a licensed well contractor and your local health department before you change the pump or drill. They can tell you how your local aquifer behaves and which rules apply where you live.

Keep one more thing in mind as you look at treatment: every gallon a treatment system sends down the drain is a gallon your well had to pump. On a well near the saltwater line, that changes which setup makes sense.

Treating Salty Well Water at the Tap

A water softener is the wrong tool here. UMD Extension explains that softeners pass water over a resin that replaces calcium, magnesium, iron and manganese with sodium, so a softener adds sodium instead of removing salt. One study it cites found that softened well water averaged 278 mg/L of sodium. If you already run a softener, our guide on whether softened water is safe to drink covers what that means for your drinking water.

The household treatments UMD Extension recommends for lowering sodium are reverse osmosis and distillation. Both treat a small volume of water at a time, so they're typically installed at one faucet, usually the kitchen sink. For a coastal well with rising chloride, that's the setup that fits: treat the water you drink and cook with, and leave showers and laundry alone unless salt is causing problems there too. If your results are very high, share them with a Crystal Quest® water specialist before you choose a system, since the right membrane depends on how salty the feed water is. Our overview of what reverse osmosis removes explains how the membrane handles dissolved salts.

Point-of-use treatment also keeps the extra load on your well small. A reverse osmosis system sends part of the water it processes to the drain, as our guide to reverse osmosis waste water explains. Kept to drinking and cooking water, that extra draw stays modest. Treat every gallon in the house and it grows with your whole household's use, which is the opposite of what a well near the saltwater line needs.

Whole-house reverse osmosis is an option when salt causes problems at every tap. It's a larger system with pretreatment, storage and more drain water, so size it from a lab report rather than a guess. Our whole-house reverse osmosis guide covers who actually needs one.

If chloride keeps climbing even with careful pumping, treatment eventually stops being the whole answer. That's when a new well location or a connection to a public water system belongs in the conversation with your contractor and health department.