Three Oscillatoria strains and one Anabaena species were isolated from three different water supply systems in California that experienced earthy-musty taste and odor problems in their drinking water. Unialgal cultures, free of actinomycetes, were purged using the Grob closed-loop stripping analysis method, and the resulting methylene chloride extracts were analyzed on a gas chromatograph/mass spectrometer. Geosmin was produced by Oscillatoria simplicissima and Anabaena scheremetievi, and 2-methylisoborneol was produced by 0. curviceps and 0. tenuis. These compounds are the two major causes of earthy-musty tastes and odors in water. In three instances, the major odorant found in culture was previously identified in the water or sediment sample from which the respective organism was isolated. 0. curviceps was implicated in a taste and odor episode involving 2-methylisoborneol in a major reservoir. Geosmin and 2-methylisoborneol were easily detected with culture samples of only 4 to 25 ml.

Nitrification in chloraminated drinking water can have a number of adverse effects on water quality, including a loss of total chlorine and ammonia-N and an increase in the concentration of heterotrophic plate count bacteria and nitrite. To understand how nitrification develops, a study was conducted to examine the factors that influence the occurrence of ammonia-oxidizing bacteria (AOB) in a chloraminated distribution system. Samples were collected over an 18-month period from a raw-water source, a conventional treatment plant effluent, and two covered, finished-water reservoirs that previously experienced nitrification episodes. Sediment and biofilm samples were collected from the interior wall surfaces of two finished-water pipelines and one of the covered reservoirs. The AOB were enumerated by a most-probable-number technique, and isolates were isolated and identified. The resistance of naturally occurring AOB to chloramines and free chlorine was also examined. The results of the monitoring program indicated that the levels of AOB, identified as members of the genus Nitrosomonas, were seasonally dependent in both source and finished waters, with the highest levels observed in the warm summer months. The concentrations of AOB in the two reservoirs, both of which have floating covers made of synthetic rubber (Hypalon; E. I. du Pont de Nemours & Co., Inc., Wilmington, Del.), had most probable numbers that ranged from <0.2 to >300/ml and correlated significantly with temperature and levels of heterotrophic plate count bacteria. No AOB were detected in the chloraminated reservoirs when the water temperature was below 16 to 18°C. The study indicated that nitrifiers occur throughout the chloraminated distribution system. Higher concentrations of AOB were found in the reservoir and pipe sediment materials than in the pipe biofilm samples. The AOB were approximately 13 times more resistant to monochloramine than to free chlorine. After 33 min of exposure to 1.0 mg of monochloramine per liter (pH 8.2, 23°C), 99% of an AOB culture was inactivated. The amounts of this disinfectant that are currently used (1.5 mg/liter at a 3:1 ratio of chlorine to ammonia-N) may be inadequate to control the growth of these organisms in the distribution system.

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A guide to confirmed geosmin- and MIB-producing cyanobacteria isolated in the United States is being prepared. This document will include 41 different species or morphologically distinct types from eight states and diverse aquatic sources isolated over a 22-year period. The organisms comprised by this guide demonstrate the importance of attached cyanobacteria as off-flavor agents, the strain specificity of MIB production, the existence of unicellular MIB producers, the occurrence of multiple geosmin and MIB producers in reservoirs, and the relationship of certain planktonic odor producers to species in other countries.

The California Aqueduct supplies water from Northern California to Southern California, dividing into the West and East branches above Pyramid Lake. In July and August 1990, elevated geosmin levels (10-48 ng/l) occurred in the East Branch of the aqueduct, which extends along the southern edge of the Mojave Desert. The geosmin episode was associated with attached algal growths on the sides of the aqueduct. A geosmin-producing cyanobacterium, possibly a Microcoleus sp., was isolated from both water and periphyton. In the summer of 1991, elevated levels of 2-methylisoborneol (MIB) occurred in the East Branch of the aqueduct (up to 78 ng/l), along with lower levels of geosmin. In July 1992, a recurrence of MIB production led to a severe off-flavor problem for a water agency that receives water directly from the aqueduct, resulting in numerous complaints from consumers. In both episodes, a Lyngbya sp. was isolated from periphyton and mud collected near the water's edge. These isolates were strong MIB producers in culture, yielding 240 and 260 μg/l, respectively. Beginning in 1992, a second, relatively weak MIB producer, a Hyella sp., was isolated from membrane-filter plates inoculated with aqueduct water. These off-flavor episodes - associated with low flows during a drought period - showed that previously untainted water sources can be affected by these problems when conditions change.