Bacteriological Analysis

Choosing a sampling port

A good sampling port or faucet is necessary to avoid false positive results where the water source may be clean but the fitting is contaminated. For this reason, avoid sampling from hoses, leaky or dirty taps etc.  Regulated water systems have pre-determined routine sampling locations where the sample must be collected. Collection should not occur when wind, dust or rain may contaminate the sample.

Sampling procedure

Sampling procedures must be followed carefully to avoid a “false positive”

• Sanitize the sampling port by thoroughly spraying the inside and outside of the sampling port with rubbing alcohol.  Wait 5 minutes.
• Run the water for 5 minutes at a moderate flow (not full force), then slow the flow to collect the sample without splashing.
• Using clean hands break the bottle seal and carefully fill the bottle past the minimum fill line (100 ml) leaving about ¹/₂ inch headspace, and re-seal the bottle. Do not touch the inside of the bottle.
• Keep bottles upright.
• The bottle label should be clearly and completely filled out with an indelible pen (Dellavalle pens work well), noting the sample ID, time, date, sampler, and analysis [“Total coliform, e. coli if present” for presence/absence analysis or “Total coliform, e. coli MPN” to test for the most probable number (MPN)]
• Place samples in a clean zip lock bag and then in a cooler.
• Fill out the Coliform Work Order.  Put properly filled out paperwork in a plastic bag. The work order should have the same information as on the bottle
• Fill cooler with lots of blue ice around and on top of the samples. Add some packing material if there is any head space to prevent bottles from rattling in transit. Hot weather may require bagged ice.
• Samples must be dropped off or shipped the same day that they are collected to meet hold times.