several times with the water to be tested and then fill with a minimum of splashing.

Surface Supplies

When sampling surface supplies, fill chemically cleaned raw water sample containers with water from the pump discharge ONLY after the pump has operated long enough to flush the discharge line. Take the sample from the pond, the lake, or the stream at the intake depth and location with a submerged sampler. Submerged samplers are equipped with automatic or manual valve systems that permit the collection of water at the desired depth.

Treatment Plants

Take samples inside a treatment plant from channels, pipe taps, or other points where good mixing is obtained. At some Navy installations, special sample taps are provided for this purpose.

Distribution System Taps

In the case of taps on a distribution system, let the tap run long enough to draw water from the main before taking samples.

BACTERIOLOGICAL EXAMINATION

SAMPLES In obtaining samples for bacteriological examination, avoid contaminating the bottle, stopper, or sample, because contamination often causes a potable water supply to be reported as nonpotable. Follow these precautions and get valid results.

Sample Containers

Use only clean, sterilized bottles furnished by the medical department of the installation or another qualified laboratory. If bottles are not available from these sources, sterilization may be carried out in emergencies. The tops and necks of sample bottles with glass closures should be covered with metal foil, rubberized cloth, or heavy impermeable paper or milk bottle cover tops before sterilization. Before sterilizing the sample bottle to be used for a chlorinated water sample, place 0.02 to 0.05 gram of thiosulfate, powdered or in solution, into each bottle to neutralize the chlorine residual in the sample. Keep the sterilization temperature under 393F (200C) to avoid decomposition of the thiosulfate.

Sampling from a Tap

When sampling from a tap, heat the outlet with an alcohol or gasoline torch for a few seconds to destroy any contaminating material that may be on the tip of the faucet. Occasionally, extra samples may be collected without flaming the faucet to determine whether certain faucet outlets are contaminated.

Flush the tap long enough to draw water from the main. Never use a rubber hose or another temporary attachment when drawing a sample for bacteriological examination from the tap.

Next, without removing the protective cover, remove the bottle stopper and hold both the cover and the stopper in one hand. Do not touch the bottle mouth or the sides of the stopper. Fill the bottle without rinsing (to avoid loss of thiosulfate). Replace the cap and fasten the protective covering carefully.

Sampling from Lakes, Ponds, Streams, and Pools

When collecting samples from standing water, remove the stopper as above, and plunge the bottle, mouth down, and hold it at about a 45 angle at least 3 inches below the surface. Tilt the bottle and allow air to escape and fill, moving it in a direction away from the hand holding it, so water that has touched the hand does not enter the bottle. Discard a quarter of the water and replace the stopper.

When collecting a sample from lakes or ponds, take the water 25 feet or more from the shore (from boat or pier) and preferably in water at least 4 feet deep. Do not collect the sample at the shore. A stream sample should be collected where the water is flowing, not from still areas. In a meandering stream, collect the sample where flow velocity is normal. Use the procedure given above for standing water samples.

When collecting water from a swimming pool, take the water from the side of the pool near the deepest part. Sample the pool while it is in use, preferably during the heaviest bathing load. Use the bottle containing thiosulfate. Fill according to the sampling procedure given above for standing water.

Q13. To ensure accurate results of water testing when collecting water samples, you should take all precautions to ensure that the samples are not in what condition?

Q14. To obtain a proper sample from a well, you should take what action first?