Part 3: Measuring Water Quality

Most coastal states measure water quality at their beaches at intervals of a few days to a few weeks. Because of their sewage treatment plant's proximity to a popular beach, Orange County Sanitation District measures water quality at several locations on the beach every weekday. Wherever sampling is done, the procedure is similar.

On the left, a man is standing ankle deep in the surf, collecting water samples in bottles at the end of a long stick. They usually collect at least 3 bottles at once, for experimental replicates (middle). One way to determine the presence of enterococcus is a chemical called enterolert (right). However, this test takes a long time - the bacteria must grow in a treated substance for a few days. Furthermore, there are different tests for each type of bacteria.

Water samples from the surf zone
Source: G Robertson, OCSD
Triplicate sample bottles
Source: JD Potts, NCDENR
Glow indicates enterococcus
Source: JD Potts, NCDENR

Identifying Bacteria

Identifying bacteria is not simple. Each type of bacterium must be identified separately, by its interactions with certain chemicals. The figure below shows one qualitative way to tell what type of bacteria are in a sample. This test does not reveal how many bacteria are in the sample - quantitative tests are even harder. Enterococcus bacteria (below, left), if put in a petrie dish with esculin, will grow colonies that appear as red spots. Coliform bacteria (below, middle), react wtih Shiffs Reagent to dye its colonies with a "golden-green sheen". Only a small fraction of all coliform bacteria are found in the guts of warm-blooded animals. These Fecal Coliforms (below, right) react with analine dye to form blue spots. What this all means is that you cannot throw all your water samples in some magic machine and count the bacteria. Instead, you have to divide your water samples into different growth media and let the bacteria reproduce for a few days. In fact, if the beach has to be closed due to high bacterial concentrations, no one will know until two days later.

with esculin
Total Coliform
with Shiffs reagent
Fecal Coliform
with analine dye

Assignment 3:

  1. Can you identify the types of bacteria that the state of California uses as indicators by putting your water in one petrie dish with a treated growth medium?
  2. If the beach is contaminated today, when will you find out?

Back to AB411 Huntington Beach Next: Federal Sewage Treatment Requirements