17.8.1  Sampling procedure from a tap or pump outlet

To obtain a representative sample of water, you should carefully follow the sampling procedure described below and illustrated in Figure 17.4. The steps are:

• Clean the tap/outlet using a clean cloth to remove any dirt.
• Open the tap and turn on at maximum flow and let the water run for 1 to 2 minutes; then turn it off.
• Sterilise the tap for a minute with the flame from a cigarette lighter, or an ignited alcohol-soaked cotton-wool swab.
• Open the tap again and allow the water to flow for 1 to 2 minutes at a medium flow rate.
• Open a sterilised bottle by carefully unscrewing the cap or pulling out the stopper.
• Immediately hold the bottle under the water jet and fill.
• While filling the bottle, hold the cap face downwards to prevent entry of dust, which may contaminate the sample.
• Place the stopper in the bottle or screw on the cap. A small air space should be left to make shaking before analysis easier.

Figure 17.4  Procedures for sampling water from a tap. (Source: WHO, 1997, Guidelines for drinking water quality, Volume 3)