RATIONALE :
Excess dissolved s o l i d s are objectionable i n drinking water
because of possible physiological e f f e c t s , unpalatable mineral
tastes, and higher c o s t s because of c o r r o s i o n or t h e n e c e s s i t y
for additional treatment.
The p h y s i o l o g i c a l effects d i r e c t l y related t o d i s s o l v e d
s o l i d s include l a x a t i v e e f f e c t s p r i n c i p a l l y from sodium s u l f a t e
and magnesium s u l f a t e and the adverse effect of sodium on c e r t a i n
p a t i e n t s a f f l i c t e d w i t h cardiac disease and women w i t h toxemia
a s s o c i a t e d w i t h pregnancy. One study w a s made using data
,. ~ e
collected from wells in North Dakota. Results from a
questionnaire showed that with wells in which sulfates ranged
from 1,000 to 1,500 mg/L, 62 percent of the respondents indicated
laxative effects associated with consumption of the water.
However, nearly one-quarter of the respondents to the
questionnaire reported difficulties when concentrations ranged
from 200 to 500 mg/L (Moore, 1952). To protect transients to an
area, a sulfate level of 250 mg/L should afford reasonable
protection from laxative effects.
As indicated, sodium frequently is the principal component of
dissolved solids. Persons on restricted sodium diets may have an
intake restricted from 500 to 1,000 mg/day (Nat. Res. Coun.,
1954). That portion ingested in water must be compensated by
reduced levels in food ingested so that the total does not exceed
the allowable intake. Using certain assumptions of water intake
(e.g., 2 liters of water consumed per day) and sodium content of
food, it has been calculated that for very restricted sodium
diets, 20 mg/L in water would be the maximum, while for
moderately restricted diets, 270 mg/L would be maximum. Specific
sodium levels for entire water supplies have not been recommended
but various restricted sodium intakes are recommended because:
(1) the general population is not adversely affected by sodium,
but various restricted sodium intakes are recommended by
physicians for a significant portion of the population, and (2)
270 mg/L of sodium is representative of mineralized waters that
may be aesthetically unacceptable, but many domestic water
supplies exceed this level. Treatment for removal bf sodium in
water supplies is costly (NAS, 1974).
A study based on consumer surveys in 29 California water
systems was made to measure the taste threshold of dissolved
salts in water (Bruvold et al., 1969). Systems were selected to
eliminate possible interferences from other taste-causing
substances than dissolved salts. The study revealed that
consumers rated waters with 319 to 397 mg/L dissolved solids as
llexcellentwlhti le those with 1,283 to 1,333 mg/L dissolved solids
were "unacceptable" depending on the rating system used. A *lgoodll
rating was registered for dissolved solids less than 658 to 755
mg/L. The 1962 PHS Drinking Water Standards recommended a
maximum dissolved solids concentration of 500 mg/L unless more
suitable supplies were unavailable.
Specific constituents included in the dissolved solids in
water may cause mineral tastes at lower concentrations than other
constituents. Chloride ions have frequently been cited as having
a low taste threshold in water. Data from Ricter and MacLean
(1939) on a taste panel of 53 adults indicated that 61 mg/L NaCl
was the median level for detecting a difference from distilled
water. At a median concentration of 395 mg/L chloride a salty
taste was distinguishable, although the range was from 120 to
1,215 mg/L. Lockhart, @t al. 1955) evaluated the effect of
chlorides on water used for brewing coffee indicated threshold
concentrations for chloride ranging from 210 mg/L to 310 mg/L
depending on the associated cation. These data indicate that a
0 level of 250 mg/L chlorides is a reasonable maximum level to \.p protect consumers of drinking water.
The causation of corrosion and encrustation of metallic
surfaces by water containing dissolved solids is well known. In
water distribution systems corrosion is controlled by insulating
dissimilar metal connections by nonmetallic materials, using pH
control and corrosion inhibitors, or some form of galvanic or
impressed electrical current systems (Lehmann, 1964). In
household systems water piping, wastewater piping, water heaters,
faucets, toilet flushing mechanisms, garbage grinders and both
clothes and dishwashing machines incure damage.
By using water with 1,150 mg/L dissolved solids as compared
with 250 mg/L, service life was reduced from 70 percent for
toilet flushing mechanisms to 30 percent for washing equipment.
Such increased corrosion was calculated in 1968 to cost the
consumer an additional $0.50 per 1,000 gallons used.
All species of fish and other aquatic life must tolerate a
range of dissolved solids concentrations in order to survive
under natural conditions. Based on studies in Saskatchewan it
has been indicated that several common freshwater species
survived 10,000 mg/L dissolved solids, that whitefish and pikeperch
survived 15,000 mg/L, but only the stickleback survived
20,000 mg/L dissolved solids. It was concluded that lakes with
dissolved solids in excess of 15,000 mg/L were unsuitable for
most freshwater fishes (Rawson and Moore, 1944). The 1968 NTAC
Report also recommended
less than that caused
chloride.
maintaining osmotic pressure levels of
by a 15,000 mg/L solution of sodium
Marine f i s h e s a l s o e x h i b i t v a r i a n c e i n a b i l i t y t o t o l e r a t e
s a l i n i t y changes. However, f i s h k i l l s i n Laguna Madre o f f t h e
Texas coast h a v e o c c u r r e d with s a l i n i t i e s i n the range of 75 t o
100 o/oo. Such c o n c e n t r a t e d seawater is caused by e v a p o r a t i o n
and l a c k of exchange w i t h the Gulf of Mexico (Rounsafell and
Everhart, 1953).
E s t u a r i n e s p e c i e s of f i s h a r e t o l e r a n t of s a l i n i t y changes
ranging from fresh t o brackish t o seawater. Anadromous species
likewise are t o l e r a n t although evidence indicates t h a t the young
cannot t o l e r a t e t h e change u n t i l t h e normal t i m e of migration
(Rounsefell and Everhart, 1953). Other a q u a t i c s p e c i e s are more
dependent on s a l i n i t y f o r p r o t e c t i o n from p r e d a t o r s o r r e q u i r e
c e r t a i n minimal s a l i n i t i e s for successful hatching of eggs. The
o y s t e r d r i l l cannot t o l e r a t e s a l i n i t i e s less than 12.5 o/oo,
Therefore, estuarine segments containing s a l i n i t i e s below about
1 2 . 5 o/oo produce most of t h e seed o y s t e r s f o r p l a n t i n g
(Rounsefell and Everhart, 1953). Based on similar examples, the
1968 NTAC Report recommended t h a t t o p r o t e c t f i s h and o t h e r
marine animals no changes in hydrography or stream flow should be
allowed that permanently change isohaline p a t t e r n s i n the estuary
by more than 10 percent from n a t u r a l variation.
Many of the recommended game bird l e v e l s f o r dissolved s o l i d s
concentrations i n drinking water have been extrapolated from data
c o l l e c t e d on domestic species such as chickens. However, young
ducklings were r e p o r t e d poisoned i n Suisan Marsh by s a l t when
maximum summer s a l i n i t i e s v a r i e d from 0.55 t o 1.74 o/oo w i t h
~ means as high as 1.26 o/oo ( G r i f f i t h , 1963).
I n d i r e c t e f f e c t s of excess dissolved solids are primarily the
elimination of desirable food plants and other habitat-forming
p l a n t s . Rapid s a l i n i t y changes cause plasmolysis of t e n d e r
l e a v e s and stems because of changes i n osmotic pressure. The
1968 NTAC Report recommended the following l i m i t s i n s a l i n i t y
variation from natural t o protect w i l d l i f e habitats:
Natural Salinity Variation Permitted
(O/OO) (o/oo)
0 t o 3.5 1
3.5 to 13.5 2
13.5 to 35 4
A g r i c u l t u r a l uses of water a r e a l s o l i m i t e d by excessive
d i s s o l v e d s o l i d s concentrations. Studies have indicated t h a t
chickens, swine, c a t t l e , and sheep can survive on s a l i n e waters
up t o 15,000 mg/L of s a l t s of sodium and calcium combined with
bicarbonates, c h l o r i d e s , and s u l f a t e s but only 10,000 mg/L of
corresponding s a l t s of potassium and magnesium. The approximate
l i m i t for highly alkaline waters containing sodium and calcium
carbonates is 5,000 mg/L (NTAC, 1968).
I r r i g a t i o n use of water depends not only upon the osmotic
effect of dissolved solids, but a l s o on the r a t i o of the various
c a t i o n s p r e s e n t . I n a r i d and s e m i a r i d a r e a s general
c l a s s i f i c a t i o n of s a l i n i t y hazards has been prepared (NTAC, 1968)
(see Table 9).
Table 9.-Dissolved Solids Hazard f o r I r r i g a t i o n Water (mg/L).
water from which no detrimental
effects w i l l usually
be noticed--------------------- 500 .-... ,,
water which can have detrimental
e f f e c t s on sensit
i v e crops--------------------- 500-1,000
water t h a t may have adverse
effects on many crops and
requires c a r e f u l managemerit
practices----------------- 1,000-2,000
water t h a t can be used f o r
t o l e r a n t p l a n t s on permeable
s o i l s w i t h c a r e f u l
management practices----------- 2,000-5,000
The amount of sodium and the percentage of sodium i n r e l a t i o n
t o o t h e r c a t i o n s a r e o f t e n i m p o r t a n t . I n a d d i t i o n t o
c o n t r i b u t i n g t o osmotic p r e s s u r e , sodium is t o x i c t o c e r t a i n
plants, e s p e c i a l l y f r u i t s , and frequently causes problems in s o i l
s t r u c t u r e , i n f i l t r a t i o n , and p e r m e a b i l i t y rates ( A g r i c u l t u r e
Handbook #60, 1954). A high percentage of exchangeable sodium i n
s o i l s c o n t a i n i n g c l a y s t h a t s w e l l when w e t can cause a s o i l
c o n d i t i o n adverse t o water movement and p l a n t growth. The
exchangeable-sodium percentage (ESP) * is an index of the sodium
s t a t u s of s o i l s . An ESP of 1 0 t o 15 p e r c e n t is c o n s i d e r e d
excessive i f a high p e r c e n t a g e of s w e l l i n g clay m i n e r a l s is
p r e s e n t ( A g r i c u l t u r a l Handbook #60, 1954).
0
For s e n s i t i v e f r u i t s , t h e t o l e r a n c e f o r sodium f o r i r r i g a t i o n
water is f o r a sodium a d s o r p t i o n r a t i o (SAR)** of about 4,
whereas for g e n e r a l c r o p s and forages a r a n g e of 8 t o 18 is
g e n e r a l l y considered usable (NTAC, 1968). It is emphasized t h a t
a p p l i c a t i o n of these f a c t o r s must be i n t e r p r e t e d i n r e l a t i o n t o
s p e c i f i c s o i l conditions e x i s t i n g i n a given l o c a l e and t h e r e f o r e
frequently r e q u i r e s f i e l d i n v e s t i g a t i o n .
I n d u s t r i a l r e q u i r e m e n t s r e g a r d i n g t h e d i s s o l v e d s o l i d s . ,-
c o n t e n t of raw waters is q u i t e v a r i a b l e . Table 10 i n d i c a t e s
Table 10.-Total Dissolved Solids Concentrations of Surface
Waters That Have Been Used as Sources for
Industrial Water Supplies
Industry/Use Maximum Concentration
( m g m
Textile 150
Pulp and Paper 1,080
Chemical 2,500
Petroleum 3,500
Primary Metals . 1,500
Boiler Make-up 35,000
maximum values accepted by various industries for process
requirements (NAS, 1974). Since water of almost any dissolved 0
solids concentration can be de-ionized to meet the most stringent
requirements, the economics of such treatment are the 1 imiting
factor for industry.
*ESP = 100 [a + b(SAR)]
1 [a + b(SAR)]
where: a = intercept respresenting experimental
error
(ranges from -0.06 to 0.01)
from 0.014 to 0.016)
b =slope of regression line (ranges
**SAR = sodium adsorption ratio = Na -
[0.5(Ca + Mg)]""
SAR is expressed as milliequivalents
(QUALITY CRITERIA FOR WATER, JULY 1976) PB-263943
SEE APPENDIX C FOR METHODOLOGY