In order to accurately test water quality, it is important to ensure the sample is prepared correctly.

The way a test sample is prepared has an impact on the result of the test. Some tests require the sample to be taken from a specific area in the water treatment process.

The most common sampling technique is a grab sample.

A grab sample tests the water at a point in time at a specific location. It doesn't indicate what the water has been like, or what it will be like in the future. It is important to collect a representative sample of the process water. The few litres of water that are collected must represent all of the water coming into the treatment process at a particular place and time. To make collecting grab samples easier and to save time, many treatment plants pump water from that the part of the process needing sampling to an on-site laboratory.

The following is a general guideline for grab sampling.