Sodium and Chloride in Drinking
Water
The compound known as "salt" consists of the elements sodium
(Na) and chloride (Cl). Many people use the word salt when intending
to refer only to sodium. Every water supply contains some sodium
and chloride.
Sodium Levels:
Sodium levels in drinking water that are less than 20 mg/L are
considered safe for most people. In the seacoast area, however,
elevated levels of sodium and chloride occur naturally due to
the proximity to seawater. Substantially higher levels of sodium
and chloride may also be due to contamination by activities of
man including: use of road de-icing salts, discharges from water
softeners, human or animal waste disposal, leachate from landfills
and many other activities.
Health Implications:
At present there are no health standards for sodium and chloride
in drinking water. A review by EPA in the mid-1980s showed that
elevated levels of sodium in drinking water did not cause high
blood pressure or heart disease, rather only that sodium should
be avoided by those people who already had such medical conditions.
It is important to note that sodium is an essential nutrient.
The Food and Nutrition Board of the National Research Council
recommends that most healthy adults need to consume at least
500 mg of sodium per day, and that sodium intake be limited to
no more than 2400 mg/day. A Food and Drug Administration publication
states that most American adults tend to eat between 4,000 and
6,000 mg of sodium per day.
When considering the health importance of sodium and chloride,
EPA assumes that water users consume two liters of water per
day and recognizes that, on average, 20 percent of a person's
daily sodium intake is from drinking water. The rest of an average
person's sodium intake is usually from food. There are no known
health concerns with chloride. Persons on a sodium-restricted
diet should evaluate all possible sources of sodium when attempting
to reduce overall intake. It is often much easier and less expensive
to make a dietary change than to excessively purify drinking
water.
EPA has recommended that sodium levels in drinking water not
exceed 20 mg/L for people on a physician-prescribed "no
salt diet". This is a very stringent level. For comparison purposes,
regular milk has a sodium concentration of approximately 500
mg/L.
High levels of sodium and chloride result in poor tasting water.
EPA has identified a concentration of over 250 mg/L above which
both sodium and chloride can be expected to impart a "salt" taste
to drinking water. This level is based on aesthetic concerns
and is only advisory in the EPA Safe Drinking Water Act program.
The main source of sodium and chloride in Whatcom County:
The most common source of significantly elevated levels of
sodium and chloride in well water in Whatcom County is seawater
from storm spray, underground intrusion or relic salt-water pockets.
Residents in these areas may choose to bathe with the water, but
use bottled or treated water for drinking, cooking and for watering
plants. The level of sodium in the water should be considered
and compared to the total intake of sodium in a person's diet.
A person on a sodium-restricted diet should avoid drinking this
water.
Control of other sources of sodium and chloride:
Normally the best method to control sodium and chloride in
drinking water is to prevent or better manage those activities
that dispose of salt near the water supply source(s). In addition
to seawater, other common sources of salt in water supplies include:
- Water softeners: Water softeners add sodium to drinking water
in two ways: during the hardness removal process, and indirectly
by the discharge of water brine into subsurface disposal systems.
The amount of salt added by ion exchange can be substantial
if a water's hardness is high.
Other sources:
Many water treatment chemicals have sodium as a basic ingredient.
These chemicals often perform a valued treatment function. However,
they do raise the sodium level in waters proportional to the
rate applied.
Treatment:
Sodium and chloride are costly to remove from water. Treatment
types include:
- Reverse Osmosis: not practical for high volume needs due
to cold water "reject" rate.
- Distillation: very costly to operate.
- Ion Exchange-Deionization: technically practical but not
often used on a large scale.
Where treatment is going to be installed, the size options range
from an under-the-sink system to full house treatment. If only
pure drinking water is your goal, then an under-the-sink system
will suffice.
The presence of elevated levels of sodium and chloride increases
the water's corrosiveness, possibly increasing damage to plumbing
fixtures. To reduce this damage, a treatment system would need
to be installed that will service the entire structure. Bottled
water is also an option to address health concerns (posed by leached
lead and copper) in the interim period while a long-term solution
is being investigated.
For more information:
E-mail us at water@co.whatcom.wa.us or
call us at (360) 676-6724. Ask to speak to an Environmental
Health Specialist in the Water Program.
Back to Top
|
