When collecting a sample for biological contaminants like total coliform, what is an important step?

Leaving a one inch gap at the top of the bottle is important when collecting a sample for biological contaminants such as total coliform because it allows for adequate air space to avoid any potential contamination or overflow during transportation. This gap helps to ensure that the sample remains uncontaminated, which is critical for accurate testing and analysis.

Additionally, this air space can prevent spillage that may occur from temperature changes or movements during transport, ensuring the integrity of the sample. It is also a common practice to leave some space to enable proper mixing if preservatives are included later or if the sample needs to be agitated before analysis.

In contrast, filling the bottle completely to the top could lead to spillage or contamination risk as mentioned, while using a sterile spoon is unnecessary for water samples, and sealing the bottle immediately after collection is important but secondary to ensuring the correct volume is maintained.