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Bacteria

These are living microorganisms that are capable of growing in 18 megohm.cm waters. They are a common cause of problems associated with high purity water systems. Regular testing enables the detection of rising levels, before they cause product loss. The most influential criteria for their presence in water coming out of a water system is the presence of low flow rates.

Testing for bacteria usually utilizes a filtration method. Filtered cells individually (or as aggregates) grow into large masses of cells. These masses are reported as “Colony Forming Units” (CFU). Specifications, describing limits for bacterial numbers at various locations in the water production and distribution system, are generally based on the current application process.

Epifluorescent (TOTAL) Bacteria Counts

Epifluorescent bacteria counts have gained acceptance as an alternative test method to viable counts. The bacteria in the water samples are filtered onto small plastic filters, stained with a fluorescent dye, and the glowing bacteria, as a result of UV light excitation, are visualized and counted utilizing a epifluorescent microscope. This method yields results in terms of total, living and dead, bacteria per 100ml of sample.

LAL (Limulus Amoebocyte Lysate) or Pyrogen Test

This is a indirect test that quantifies the gelatinous, polysaccharide matrix that surrounds the gram negative bacteria (most bacteria in the ultrapure water system). Since there is no average amount of polysaccharide associated with each cell, the test results are given as Endotoxin units/milliliter (Eu/ml) of water.

Contaminant	Problem	Cause	Possible Cure
Bacteria	High port counts	Dead leg Bad port	Shorten leg, Increase flush time until ok Replace port
	High at point of use	low flow	Bigger pump Reduce back pressure
	High tank counts	tank too large	Smaller tank Higher flow rates Nitrogen blanket Ozone layer