Taste & Odor Problems in
Drinking Water
NMED Drinking Water Bureau
Overview
• There are several possible causes of taste and
odor problems in drinking water, the most
common include:
– Chlorine
– Iron and Manganese
– H2S in source water
– Stale water
– Algae
• Many T&O compounds have very low thresholds
Drinking Water Bureau
Overview
• Most T&O compounds are not a health
concern, but some can be.
• T&O problems may create the perception
that water is not safe to drink.
• It’s important to not only address the T&O
problems, but also to have a public
relations strategy.
Drinking Water Bureau
Overview
Taste/Odor
Chemical
Source
Chlorine taste & odor
Chlorine
Too much chlorine
Chlorine odor
Chloramines
Chlorine below breakpoint
Fruity odor
Aldehydes
Ozonation
Rusty or metallic
taste
Iron
Naturally occurring,
corroded pipes
Rusty or metallic
taste
Manganese
Naturally occurring
Sulfur taste and odor
Hydrogen Sulfide
Naturally occurring
Musty taste and odor
Geosmin
Blue-Green Algae
Musty taste and odor
2-Methylisoborneol
(MIB)
Blue-Green Algae
Fishy, grassy
Various
Algae
Drinking Water Bureau
Chlorine
Zone 1: Chlorine
consumed by reducing
compounds (e.g. H2S)
Zone 2: Formation of
chloramines and
chlorinated organics.
Chlorine odor.
Zone 3: Chloramines and
organics partly destroyed.
Zone 4: Residual formed.
Too much residual →
chlorine taste & odor
Drinking Water Bureau
Iron & Manganese
• Water with dissolved iron (Fe) or manganese
(Mn) may appear clear at first, but may form red
or black particles as it oxidizes.
• Fe and Mn can exist in suspended or colloidal
form which will give water a tint.
• Fe can form reddish-brown stains. Mn can cause
brownish-black stains.
• Fe and Mn can build up in pipelines and tanks.
• Secondary standards Fe, Mn: .3mg/l, .05 mg/l,
Drinking Water Bureau
Iron & Manganese
Removal of Fe and Mn:
• Test to identify types and concentrations of Fe/Mn
• Oxidation/filtration is most common approach for
dissolved Fe/Mn.
– Cl is a common oxidant, but could cause DBPs
– Other oxidants, e.g. Potassium permanganate
(KMnO4), can be temperamental
• Ion exchange can be used for low concentrations
of Fe/Mn (~5 mg/l combined)
Drinking Water Bureau
H2 S
• Hydrogen Sulfide (H2S) in drinking water
generally does not pose a health risk at
low concentrations.
• Often occurs naturally, but can be caused
sulfur-reducing bacteria in wells.
• Taste and odor threshold is ~ 100 ppb
Drinking Water Bureau
H2 S
• Shock chlorination can kill sulfur-reducing
bacteria in wells.
• There are a variety of ways H2S can be
removed from water, depending in part on
concentration:
– Aeration
– Manganese Greensand
– Oxidation (e.g. chlorination)
Drinking Water Bureau
Water Age
• There is a correlation
between water age
and deteriorated
water quality.
• Water age is a
function of demand,
system design and
system operation.
Drinking Water Bureau
Water Age
• Water quality can change over time:
– Lower chlorine residual
– Increased bacterial growth (biofilms)
– Changes in temperature, pH, dissolved O2
– Precipitation of minerals
– Increased disinfection byproducts
– Taste & odor problems
Drinking Water Bureau
Water Age
• Considerations for reducing water age
problems:
– Eliminate dead ends
– Have a flushing program
– Don’t over design your system
– Tank management
– Replace deteriorated pipe
Drinking Water Bureau
Algae
• Algae is a large diverse
group of photosynthetic
organisms.
• It is possible to have
several types of algae
growing together.
• Algae requires light and nutrients to grow
in water. Many prefer warmer water.
Drinking Water Bureau
Algae
• Many species of algae produce volatile
organic compounds (VOCs) that can result
in taste and/or odor in water.
• Tastes and odors can include fruity,
musty, fishy, grassy, banana, glue, acrid.
• Some VOCs are produced and excreted
during growth, others released when cell
dies or is damaged.
Drinking Water Bureau
Algae
Cyanobacteria
• AKA blue-green algae.
• Actually a bacteria.
• Several cyanobacteria
produce cyanotoxins.
• Microcystin is the most common cyanotoxin.
• World Health Organization provisional guideline
for Microcystin is 1 μg/l (1 ppb) in drinking water.
Drinking Water Bureau
Algae
Cyanobacteria
• Many cyanobacteria produce
taste and odor compounds.
• Most common T&O
compounds are Geosmin
and 2-methylisoborneol
(MIB) → musty T&O
• MIB and Geosmin are not toxic, but some
cyanobacteria produce these and toxins. Some
produce toxins, but no T&O compounds.
Drinking Water Bureau
Algae
Cyanobacteria
• Geosmin
– odor threshold is ~5 ng/l (parts per trillion or ppt)
– taste threshold is ~16 ppt
• MIB
– odor threshold is ~15 ppt
– taste threshold is ~18 ppt
Drinking Water Bureau
Algae
There are several other problematic groups
of algae including:
• Chrysophyta – can form blooms and give
off a strong fishy odor
• Chlorophyta – AKA “Green Algae”. Can
form blooms and add a lot of organics to
the water. Taste and odor generally
grassy, but can be fishy.
Drinking Water Bureau
Algae Growth
Conditions leading to algae growth:
• Algae are naturally
occurring.
• Algal blooms usually result
from excess nutrients,
primarily phosphorous
(possibly nitrogen).
• Nutrient sources include farm and range
runoff, wastewater.
Drinking Water Bureau
Algae Growth
Conditions leading to algae growth:
• Blooms usually occur in summer
• Cyanobacteria generally like calm water
so they can position themselves in the
optimal location in the water column.
Drinking Water Bureau
Algae Growth
Treatment plant issues
• If clarifiers are not enclosed, algae growth
can occur within the clarifiers
• Excess algae can clog filters
• Pretreatment with an oxidant will kill the
algae and release T&O compounds.
• The algae and T&O compounds can
increase DBP production.
Drinking Water Bureau
Algae Monitoring
• Monitoring Program may
include:
– Algae species
– T&O compounds
– Toxic compounds
– Nutrients
• Take a progressive approach to identify
problematic portions of system, causes,
species, compounds.
Drinking Water Bureau
Algae Monitoring
• To collect planktonic
(free floating) algae for
ID, need to find right
location, depth and time.
• Higher concentrations of algae may be
below surface so may need ability to sample
at depth.
• Use Secchi disk to determine photic depth.
Drinking Water Bureau
Algae Monitoring
• Monitoring program will alert the system to
when algae concentrations increase.
• Water systems should know if there are
cyanotoxins in the water in addition to
T&O compounds.
• Only a few labs ID algae and test for MIB,
Geosmin or cyanotoxins.
Drinking Water Bureau
Algae Control
• Goal is to limit algae growth
• Prevent excess nutrients in watershed, i.e.
source water protection
• Artificial mixing in reservoirs to prevent
cyanobacteria growth.
• Kill algae with an algaecide such as
copper sulfate.
Drinking Water Bureau
Algae Control
Source Water Protection
• Try to reduce nutrient input
• Requires working with agricultural and
wastewater sources upstream and limiting
erosion.
• Difficult to do if watershed is large and/or
lots of inputs.
Drinking Water Bureau
Algae Control
Artificial Mixing
• Disrupts
Cyanobacteria
depth control
• May deceases light
penetration
• Could cause other algae to increase
• Could increase turbidity
• Could cause other chemical changes
Drinking Water Bureau
Algae Control
Algaecide
• Copper Sulfate (CuSO4) is
most common
• Cost ~ $10/acre per application
• Very short lived. Reacts with minerals and
precipitates. May require multiple applications.
• Toxic to fish.
• Killing algae will release internal T&O/toxic
compounds. CuSO4 should only be used to prevent
algae blooms.
Drinking Water Bureau
Climate
• Climate in New Mexico
is predicted to get
warmer with lower
spring runoff.
• These conditions will
favor the development
of algae blooms.
• Warmer temps could make other T&O problems
worse such as chlorine or stale water.
Drinking Water Bureau
Public Notification
• When there is a taste or odor problem,
some members of the public will assume
the water is unsafe.
• Be proactive. Let them know
– What the problem is
– Cause of the problem
– Health implications
– Duration
– What the system is doing about it
Drinking Water Bureau