Practical training in the section "Hygiene of water supply of settlements"

Sampling of water from the well for sanitary-chemical analysis is done by lowering the well below the water level on the cord clean washed bottles 1 l Water scoop from the depth of 0.5 m from the surface of the water, washed bottle 2 times, then filled almost to the top and covered with cork.
A water sample for bacteriological tests selected in sterile vessel with proper precautions designed to prevent the inclusion in the studied water of bacteria from outside (with hands, from the air).
When taking samples of water from water supply pre water down during 3-5 min
The water sample is attached cover form, which indicates the location of the water source, day, hour sampling and by whom it was taken.
Selection of doses for chlorination method three glasses. For preparation of 1 % solution of bleach beat in a porcelain mortar 1 g of bleach. The mortar is poured 5-10 ml of distilled water and triturated pestle bleach, then the liquid is poured into a measuring cone with a volume of 100 ml with a glass tube. To draft in a mortar again poured 5-10 ml of water, grind and poured in a flask. Do that a few times and then bring the level of water in the flask to 100 ml. Content mix, give fluids to settle and then use it to chlorination.
In the field dosing of chlorine is produced by experienced water chlorination three glasses. In each of the three glasses pour 200 ml of water. In each glass is placed on a glass rod and drop pipette add: 1 Cup 2 drops in the 2 nd - 4 drops in the 3rd - 6 drops prepared with 1% solution of bleach. After that, the contents of glasses mix well and leave to stand for 30 minutes 30 minutes each glass determine the amount of residual chlorine. To do this, add 5 drops of 5% solution of potassium iodide 1 ml of hydrochloric acid (1 : 3) and 1 ml of 1% solution of starch, mix and monitor the occurrence of blue color. The color appears in the glasses, and free, unencumbered chlorine. For calculation of the required dosage of chlorine it is necessary to choose the glass, which contains 0.3-0.5 mg/l of free chlorine.
The amount of residual chlorine determined by titration of the burette with antinormal a hyposulphite solution, every inch of which corresponds 0,355 mg of chlorine. Titrated to bleaching liquid, carefully mixing glass rod after adding a drop of hyposulphite.
Example of calculation. In the 1st glass painting has not happened (no residual chlorine). In the 2nd and 3rd glasses appeared dark blue respectively weak and significant intensity.
During the titration 200 ml of water in the 2nd glass painting disappeared after you add 0.1 ml of 0.01% solution of hyposulphite. Consequently, on 1 l of water will be 0,1x5=0.5 ml of hyposulphite solution. If 1 ml of 0.01% solution of hyposulphite corresponds 0,355 mg chloride, 0.5 ml his will match 0,5x0,355=0.18 mg of chlorine per 1 liter
After chlorination by GOST residual chlorine should be 0.3-0.5 mg/L. Consequently, the residual chlorine in the 2nd Cup is not enough. So titration of free chlorine in the 3rd Cup. Suppose that in this case the disappearance of blue color came after adding 0.25 ml of 0.01 % solution of hyposulphite, which corresponds to 0.25 X 0,355=0.375 mg residual chlorine on 1 l of water.
This residual chlorine is responsible norm, therefore, to select the required dose of chlorine take the 3rd Cup. On 200 ml of water is added 6 drops of bleach solution, therefore, on 1 l will need 6 X 5 = 30 drops, i.e. 1,5 ml
Knowing required amount of 1% chlorine solution of this sample for 1 l of water, you can convert any number of water. So, per 1000 litres of water will need 1,5x1000=1.5 l of chlorine solution.
If experienced after chlorination blue staining occurs in 1 glass and residual chlorine exceed 0.3-0.5 mg/l, then repeat the experience with smaller doses of bleach; if none of the glass is not detected residual chlorine (large chlorine-water demand), then repeat the experience with large quantities of 1 % solution of bleach.