Hach DR/850 Procedures Manual page 21

CHEMICAL ANALYSIS INFORMATION
Collecting Water Samples
Obtain the best sample by careful collection. In general, collect samples
near the center of the vessel or duct and below the surface. Use only clean
containers (bottles, beakers). Rinse the container several times first with
the water to be sampled.
Take samples as close as possible to the source of the supply. This lessens
the influences of the distribution system on the sample. Let the water run
long enough to flush the system. Fill sample containers slowly with a
gentle stream to avoid turbulence and air bubbles. Collect water samples
from wells after the pump has run long enough to deliver water
representative of the ground water feeding the well.
It is hard to obtain a truly representative sample when collecting surface
water samples. Obtain best results by testing several samples. Use
samples taken at different times from several locations and depths. The
results can be used to establish patterns for that particular body of water.
Generally, as little time as possible should elapse between collecting the
sample and analyzing it.
Depending on the test, special precautions in handling the sample may be
necessary. This prevents natural interferences such as organic growth or
loss or gain of dissolved gases. Each procedure describes sample
preservatives and storage techniques for samples that are held for testing.
, continued
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