Sodium in Tap Water: The 20 mg/L Guidance, Water Softeners, and Road Salt

Sodium in tap water has no enforceable federal limit. EPA’s guidance level is 20 mg/L, but that number is meant only for people whose doctors have put them on a very strict diet of 500 mg of sodium a day. EPA says it should not be applied to everyone. For most people, the sodium in tap water is small next to what they eat. The main reasons levels rise are home water softeners that use salt, road salt washing into groundwater and streams, and natural geology. If you’re on a low-sodium diet, check your utility’s water quality report and talk to your doctor.

What the 20 mg/L number actually means

EPA’s sodium guidance comes from a 2003 drinking water advisory and appears in its Drinking Water Standards and Health Advisories tables. Two numbers matter:

20 mg/L is a health-based value for people restricted to a total sodium intake of 500 mg per day. EPA’s advisory says this value “should not be extrapolated to the entire population.”
30 to 60 mg/L is the level EPA recommends staying under to avoid taste problems. EPA notes that sodium in this range is unlikely to taste salty to most people, and that at 2 liters a day it would supply only about 2.5% to 5% of a daily dietary goal.

Neither number is enforceable. In the same advisory, EPA says drinking water does not play a significant role in sodium exposure for most people.

For scale, the FDA advises adults to keep total sodium under 2,300 mg a day and says the average American eats about 3,400 mg. Water with 20 mg/L of sodium, at 2 liters a day, adds about 40 mg.

New York’s drinking water rules add a second advisory value: water above 270 mg/L should not be used for drinking by people on moderately restricted sodium diets, and water above 20 mg/L should not be used by people on severely restricted diets.

Who should pay attention

For most healthy people, sodium in tap water isn’t a meaningful health concern. The people who should check are:

Anyone told by a doctor to follow a very low sodium diet
People being treated for sodium-sensitive high blood pressure. EPA’s advisory says they should talk with their health care provider about the sodium in their water and whether to use another water source or treatment at the tap.
Households with high blood pressure that drink softened water. Minnesota’s health department says to consult a doctor about drinking softened water if someone in your home has a history of high blood pressure.
People whose water is noticeably salty or whose well is near a busy salted road

Your doctor decides what your sodium target should be, not your water report. Bring the number to your next appointment.

Where the sodium comes from

Water softeners

This is often the biggest source, and it’s inside your own house. A softener that uses sodium chloride swaps the calcium and magnesium that make water hard for sodium. Minnesota’s health department says a softener using salt increases the amount of sodium in the water you drink.

How much depends on how hard your water was. Nebraska Extension, citing the Water Quality Association, says softening adds about 8 mg/L of sodium for each grain per gallon of hardness removed. Water with 10 grains per gallon of hardness would have about 80 mg/L of added sodium after full softening. Very hard water can end up well above the 20 mg/L guidance once softened, even if the utility’s water is low in sodium.

That means the sodium figure in your utility’s report doesn’t reflect your tap if you have a softener. To learn more about softening, see hard water explained and water softener vs. water filter.

Road salt

In cold climates, salt spread on roads washes into soil, streams and aquifers. USGS reports that chloride, sodium and dissolved solids are the most common contaminants with increasing concentrations across its groundwater trend networks in the US, and that in many areas the increases are directly linked to road-salt application.

USGS studies of individual sites show the risk is highest for shallow wells close to salted highways. In one Indiana study, chloride exceeded EPA’s secondary standard of 250 mg/L in late winter through summer only in very shallow wells near the highway. Chloride is the part of road salt most often measured, but sodium travels with it.

If you have a private well near a major road, a parking lot or a salt storage area, test for sodium and chloride. Our well water testing guide covers what to include.

Natural sources and treatment

Sodium is one of the most abundant elements on Earth, and EPA notes it is found in virtually all water. Some groundwater picks up more of it from the soil and rock it passes through. Your utility’s report is the best way to know what’s in your supply before it reaches your home.

Reading your water quality report

Every community water system publishes an annual Consumer Confidence Report. Here’s how to find sodium:

Look beyond the regulated contaminants table. Because sodium has no enforceable limit, it often appears under “unregulated contaminants,” “secondary standards” or “other substances.”
Check the units. Sodium is usually reported in mg/L, which is the same as parts per million (ppm).
Look for a range. Systems with several wells or sources may report a low and high value. Your home may get water from one source more than another.
Compare to 20 mg/L if you’re on a 500 mg/day diet, and share the number with your doctor.

Behind the scenes, federal rules require public water systems to test for sodium: every year for systems that use surface water, and at least every three years for groundwater-only systems. The results must be reported to the state and sent to local and state public health officials, which EPA says gives the public health community information on sodium levels in drinking water.

If you can’t find sodium in your report, call your utility. You can also find your utility through our ZIP code search and read its full report. Our guide on how to read your water quality report walks through the rest of the document.

How to lower the sodium in your drinking water

If you have a softener:

Keep an unsoftened tap for drinking and cooking. Minnesota and Nebraska Extension both suggest a bypass line, usually to the kitchen cold tap.
Switch to potassium chloride to regenerate the softener. Minnesota lists this as a way to reduce sodium. Potassium is then exchanged instead of sodium. If you have a health condition, ask your doctor before switching.
Soften only the hot water, another option Nebraska Extension describes.

If your source water is high in sodium:

Reverse osmosis. New York’s health department lists reverse osmosis among treatment methods for sodium and chloride. Keep in mind that RO also removes minerals and sends some water down the drain, which adds to the load on a septic system. Under-sink and countertop RO units treat water for drinking and cooking only. If you buy one, check the certifier’s listing for the specific claims you need, such as total dissolved solids reduction.
Bottled water with a low sodium content is another option for people on strict diets. Check the label.

Bottom line

Sodium in tap water is a concern for a small group of people, mainly those on very low sodium diets. EPA’s 20 mg/L guidance is for them, not for everyone. If you have a water softener, your tap likely has more sodium than your utility reports, and keeping an unsoftened drinking tap is the simplest fix. If your well is near a salted road, test it. And if you’re on a restricted diet, look up your sodium level and share it with your doctor.