Manatee County Water System Odor and Taste Related Aesthetic Issues
Produced by the Manatee County Water Treatment Plant Quality Control Laboratory
The odor and taste of drinking water are often the primary characteristics upon which
consumers base their judgment of the water quality. There are many constituents, which
when dissolved in water, will affect its odor or taste. While there are methods available
for quantifying many of these constituents, overall odor and taste, in both quality and
intensity, remain a subjective measure. Water that is “funny tasting” or has an “awful
smell” to some is viewed as unremarkable by others, and odor and/or taste that are
different from what one is accustomed are often judged unfavorably.
Manatee County
provides drinking water that meets all safety standards and strives to provide drinking
water to each tap in our system that is free from unfavorable odor or tastes. Our
experience with customers has shown that due to the subjective nature of odor and taste
and other factors listed below that there are a few categories which encompass the vast
majority of their odor and/or taste concerns. The information below describes some of
these concerns, details possible causes, and for some, provides diagnostic procedures that
can be performed by homeowners. Also, the Manatee County Water Treatment Plant
Quality Control Laboratory provides sample collection and analyses for Manatee County
customers with all types of water quality concerns.
If you have other non-odor or taste
water quality concerns, or further questions not answered by the information below, call
(941) 746-3020 Ext. 5014 to speak with Laboratory personnel.
“CHLORINOUS”, “BLEACH”, or “CHEMICAL” ODOR
These odors are
attributable to the residual disinfectant that is required in all distribution systems by Safe
Drinking Water Act regulations. Manatee County utilizes chloramines (chlorine +
ammonia) as a disinfectant. Chloramines are much less reactive compounds than free
chlorine (bleach), and create fewer disinfection by-products. Chloramines have a
different odor than free chlorine. Many people who have experienced water systems that
use free chlorine do not attribute any odor to chloramines, while others are sensitive to
the ammonia component of chloramines.
The chloramine concentration in your water will
vary depending on the distance you live from the Water Treatment Plant and the time of
the year. Generally, higher concentrations are found closer to the plant during the winter.
This is due to the water having a shorter residence time in the pipe (shorter distance and
higher flows) and lower water temperatures.
Conversely, the lowest levels will occur at
the ends of the system, in the summer (rainy season, winter residents gone) when water
temperature is high (can reach 92oF). As chloramines “disinfect” the water, they are
broken down and some free ammonia is formed. Water with elevated free ammonia
levels are often described as having a “chemical taste”. Because of this variability, water
at one home may not have the same degree of “chlorinous” taste as water from another
part of the County.
“EARTHY”, “MUSTY”, or “MOLDY” ODOR
These odors/tastes are primarily
caused by algae and bacteria that grow naturally in all lakes, including Lake Manatee, the
source for approximately two thirds of the County’s water. Certain algae and bacteria
produce compounds (MIB and geosmin) as part of their metabolism that impart the
earthy/musty odor/taste to the water. (These same compounds are produced by bacteria in
soil and make “dirt smell like dirt”.) The compounds do not affect the safety of the water
but produce odors at very low levels (part per trillion).
The causatory algae blooms are
episodic; they appear most frequently in the late spring and early summer but can occur
at anytime during the year. On average they occur 2 to 3 times per year and last 2-4
weeks each. Most of the time the Water Treatment Plant can adjust treatment to remove
these compounds to below threshold levels. However, during drought conditions (like in
2006 and 2007), the odorants can reach levels that exceed our capability to remove them.
Typically, if you are experiencing this odor in your water, it is occurring throughout the
system.
“SULFUR”, “SEWER” OR “ROTTEN EGG” ODOR
The rotten egg odor is caused
by the presence of hydrogen sulfide (H2S). At normal temperatures H2S is actually a gas
that can dissolve in water. In water, H2S is usually produced by a type of bacteria, sulfate
reducing bacteria (SRB), that use sulfate from the water in their metabolism and convert
it to H2S. There are several situations that could cause the detection of H2S and a little
investigative work can rapidly help diagnose the cause.
In our system, the vast majority of H2S reports by customers are actually caused by odors
from drains as opposed to odors in the tap water. Water that sits in the trap under a sink
typically contains bacteria which are capable of producing H2S. The H2S exists in
equilibrium as a gas in the drain pipe above the water and dissolved in the water in the
trap. When a customer turns on their tap and water goes down the drain, this equilibrium
is disturbed and the air in the drain containing this H2S is displaced, resulting in H2S
moving up through the drain and into the air above the sink. Because H2S is a gas, it can
disperse throughout a bathroom in a few seconds, making the whole room smell like
"rotten eggs". The longer water sits in a trap and is undisturbed, the more time the
bacteria have to produce H2S, and the more intense the odor can be.
Often customers will
report the odor is most intense when the water is first used in the morning, when they turn
the water on and then bend over to wash their face or brush their teeth.
A quick way to
determine if this is the cause of the odor is to capture the first water out of the tap in a
cup, without letting any go down the drain, and then smelling the water in the cup. If
there is no H2S odor the problem is probably with the drain.
Letting some water go down
the drain and checking for the odor can confirm the source of the odor. If the odor is
coming from the drain, there are two things that can be done to eliminate the odor
causing bacteria from the trap:
- Put two tablespoons baking soda down the drain with
an ounce or two of water (run faucet for 2-3 seconds); let it stand in drain for several
hours, then flush trap by letting faucet run for about ten seconds. This will often take a
repeat application to completely eliminate odor.
- Or pour 1/4 cup of household bleach
into the offending drain; let it stand for about 15 minutes, and then flush by letting the faucet run for about 15-30 seconds. The bleach treatment is usually more effective, but
there may be residual bleach odor for a day or two.
The second most common source of H2S odors, is the water heater. Some species of SRB
can grow in a water heater if the temperature is not set above 138 degrees, or if the water
heater is unused for an extended period. Typical chlorine disinfectant levels in
community water systems will keep SRB from growing, but the chlorine disinfectants are
reactive, and will dissipate after a couple of weeks. It's relatively easy to determine if the
problem source is the water heater, by checking the cold water and the hot water for odor.
If you have single handle "mixing type" valves, be sure to move it all the way to the cold
side and then all the way to the hot side when checking for odor.
Since you've determined
that the problem is not from the drains, it is okay to let the water run, but you should
collect a sample in a cup to check for odor. If the source is the water heater, the odor will
get stronger and persist as hot water from the water heater gets to the faucet. (You may
want to take the cup out of the room to check for odor to ensure you’re not detecting
"background" odors).
Additionally, if the water heater is involved, the odor will be from
every hot water tap in the home. To correct, the water heater should be drained and
flushed. It is also recommend that you check the thermostat setting, because many new
installs have the thermostat set at less than 120 degrees. Some customer's have set the
thermostat to 150 degrees for a couple of days when they first return from an extended
absence to "clean" the hot water lines and then set it back to 135 - 140 for routine use.
An additional source of H2S odors that we have seen over the last several years is an SRB
biofilm growth on the inside of certain flexible, plastic supply lines. These are the lines
that connect the cold and hot water lines that extend from the wall to the sink faucets.
Most of the lines where this has been documented are white in color and have an integral
push-pull valve attached. The vast majority of installations of these type lines do not
experience this problem, nor have we documented this problem in non-plastic supply
lines. Characteristic to this problem are odors that occur in the “first draw” from a sink
faucet and quickly disappear from the water as the water is run (the odor may remain in
the room as H2S is a gas). Most of the time the odor is not detected from typical shower
or tub installations as the CPVC or copper is plumbed directly to the valves with no need
for the flexible supply lines.
As with odor from the drains, the longer the water sits in the
supply line (the longer the period between uses), the greater the chance the H2S odor will
return. To determine if this is the problem, collect the first cupful (6-8 oz.) of water from
the faucet and try to detect if the odor is in the cup. Then collect the second cupful and
check for odor. Repeat with a third and fourth cup if necessary. If an SRB biofilm on the
supply lines is the cause, the odor will be present in the first cupful and will typically be
completely gone by the third cupful. Check each line independently, hot and cold
(remember to push single lever mixing-type faucets all the way to cold and then all the
way to hot when checking each side).
We have investigated cases of side by side sinks in
a bathroom where one sink has the problem and the other does not, or where only the
cold line has the problem and the hot does not. A manufacturer of the one-piece, white
flexible supply lines with plastic push-pull valve recommends a 3x3x3 flushing program
to clear the lines. They suggest flushing each offending line for 3 minutes, 3 times day,
for 3 days, being sure to only flush one at a time to insure maximum flow and scour through the line. Some of our customers have elected to replace the offending supply
lines.
Another source of H2S, of which we see with decreasing regularity, is a cross connection
with an irrigation system. Many irrigation systems rely on shallow or intermediate
aquifer wells that have elevated H2S levels. This cause can be tricky to isolate, but can be
identified by shutting the water off at the potable meter and then checking to make sure
there is no flow at the faucets. If the irrigation system is a pressure system and there is a
cross connection there should be flow. If it is not a pressure system, with the potable
water shut off, turn the pump on and check for flow. Any flow in these situations should
have the characteristic H2S odor and indicates a cross connection, which must be
immediately disconnected.