For how long must physical, chemical, and radiological sample analysis results be kept?

The correct duration for retaining physical, chemical, and radiological sample analysis results is 10 years. This requirement aligns with regulations and guidance that mandate the retention of these records to ensure accountability, traceability, and availability for inspection purposes.

Having these results on hand for a decade allows water treatment facilities to maintain compliance with legal standards, effectively respond to audits, and conduct historical comparisons that can inform future operational decisions and improvements. This period also serves to protect public health by ensuring that any potential issues can be traced back through comprehensive long-term records. Keeping data for less time could undermine these objectives, as it may not provide sufficient historical context for assessing changes in water quality or for responding to regulatory inquiries.