What characteristic is essential for sampling bottles used in testing?

The essential characteristic for sampling bottles used in testing is that they must be clear and untainted. This is critical because clarity allows for the observation of the sample, enabling the testing personnel to visually assess any particulates or contaminants that may be present in the water. Additionally, using untainted bottles ensures that no external substances interfere with the water sample, preserving the integrity of the testing process. Any contamination from the bottle itself could lead to inaccurate results, making it essential that the materials used are free of impurities that could leach into the sample.

In contrast, non-disposable bottles may not be as crucial a characteristic; while durable bottles are beneficial, they must also maintain clarity to ensure accurate observations. Heavy-duty materials could offer protection during transport, but if they aren't clear, they would fail to fulfill the primary purpose of being able to visually evaluate the sample. Colored bottles could potentially hinder visual assessments and are not typically used for water testing, where transparency is vital for detecting contamination.