Collection and Preservation of Water and Wastewater Samples

• The objective of sampling is to collect a portion of material small enough in volume to be transported conveniently and yet large enough for analytical purposes while still accurately representing the material being sampled.

General Requirements

• Handle sample so that it does not deteriorate or become contaminated or compromised before it is analyzed.
• Ensure sampling equipment are clean and quality assured before use.
• Use sample containers that are clean and free of contaminants.
• Fill sample containers with/or without prerinsing with sample.
• Composite samples can be obtained by collecting over a period of time, depth, or at many different sampling points.
• Make a record of every sampl7-sample collected and identify every bottle.
• Label bottles and document sufficient information for sample identification.

Types of samples

1. Grab Samples:

• single samples collected at a specific spot at a site over a short period of time (typically seconds or minutes).

2. Composite Samples:

• Provides a more representative sampling in which the concentration of the analytes of interest may vary over short periods of time and/or space.
• Can be obtained by combining portions of multiple grab samples or by using specially designed automatic sampling devices

Sample Container

• Collect samples in a glass or plastic bottles that have been cleansed and rinsed carefully, given a final rinse with deionized or distilled water, and sterilized.
• Volume of the sample should be 100 ml or more.

Preservation and Storage

• Start microbiological examination of water samples as soon as possible after collection.
• Analyze samples on day of receipt whenever possible and refrigerate overnight if arrival is too late for analyzing on same day.
• Do not exceed 30h holding time from collection to analysis for Coliform bacteria.
• Do not exceed 8h holding time for heterotrophic plate counts (Standard plate counts).