Which precautions should be considered when measuring the turbidity of water?

Discard scratched or etched sample tubes
Fill the tubes with samples and standards that have been agitated thoroughly, and allow sufficient time for bubbles to escape.
Sample tubes must be kept scrupulously clean, both inside and out
Turbidity of a sample an change after the sample is collected and shaking the sample will not re-create the original turbidity.
Turbidity should be measured in a sample as soon as possible to obtain accurate results.

PG 574