12.6.1  Procedure for sampling from a tap or pump outlet

To obtain a representative sample of water, the sampling procedure described below and illustrated in Figure 12.5 should be followed. The steps are:

1. Clean the tap/outlet using a clean cloth to remove any dirt.
2. Turn on the tap and let the water run at maximum flow for 1 to 2 minutes; then turn it off.
3. Sterilise the tap outlet for a minute with the flame from a cigarette lighter or an ignited alcohol-soaked cotton-wool swab.
4. Turn on the tap again and allow the water to flow for 1 to 2 minutes at a medium flow rate.
5. Open a sterilised bottle by carefully unscrewing the cap.
6. Immediately hold the bottle under the water jet and fill.
7. While filling the bottle, hold the cap face downwards to prevent entry of dust, which may contaminate the sample.
8. Screw on the cap. A small air space should be left so that the contents can be shaken more easily before analysis.

Figure 12.5  Procedure for sampling water from a tap. (WHO, 1997)