62 



WATER SUPPLY 



TOPIC 2. HOW COMMUNITIES OBTAIN PURE WATER 



SUGGESTED PROBLEMS AND QUESTIONS 



1. How do persons who live in the country or in 

 small towns secure an adequate water supply? 



2. How are the inhabitants of large cities sup- 

 plied with pure water? 



3. Of what importance is pure water to the 

 health of a community? 



SUGGESTIONS AND HELPS FOR STUDY 



1. The study of this topic should make it possible 

 for you to get a general idea of how pure water is ob- 

 tained by people living in several types of communi- 

 ties. 



2. During the study of this topic you should make 

 a detailed study of your own water supply and com- 

 pare it with the methods used in other places. 



3. To make it possible for you to compare your 

 water supply with others used, this topic will deal 

 with types of water supply such as those used in 

 rural districts and those used in towns and cities. 



4. You may find the following new words in this 

 study : 



precipitate a solid, insoluble substance formed in a so- 

 lution. 



baffle a device used to break the flow of water or turn 

 it in another direction. 



sludge mud or mire. 



EXPERIMENTS OR DEMONSTRATIONS WHICH WILL 

 HELP ANSWER THE PROBLEM QUESTIONS 



Experiment 43. How do settling basins work? 



Stir some mud and dirt with water and pour some of it 

 into a tall jar or fruit can. Observe the mixture after it has 

 stood for several hours. 



In your notebook 1 answer the following questions. What 

 happened in the jar? Was all the suspended matter affected 

 by this process ? What still remained in the water at the 

 top of the jar? Can you suggest a means for removing this 

 without filtering? 



Experiment 44. Do chemicals aid the settling of sus- 

 pended matter in water? 



a. Dissolve a small amount of iron sulphate (green 

 vitriol) in a test tube half-full of water and add a little of it 

 to some clear limcwater. 2 Allow the mixture to stand for 

 some time. Observe what happens and record your observa- 

 tions in your notebook. 3 



b. Dissolve a little aluminum sulphate (alum) in a test 

 tube half-full of water. Place some clear limewater in 

 another test tube and add half of the aluminum sulphate 



1 See workbook, p. 25. 



' Prepare limewater by stirring unslaked lime into a jar of 

 water. Allow it to stand awhile and then pour off the clear 

 limewater. 



3 See workbook, p. 25. 



solution to it. If the test tube is now warmed gently the 

 desired action will take place more quickly. Allow the tube 

 to stand undisturbed for some time. Record your observa- 

 tions in your notebook. 



c. Stir some mud with water and place some of the mix- 

 ture in a tall jar such as a fruit jar. Add about a quarter 

 teacup full of limewater to this and then about the same 

 amount of iron sulphate solution. Allow to stand for some 

 time until the settling of the green precipitate is completed. 

 Siphon the partly clear water from above the settled matter 

 and place in another tall jar. To this add more limewater 

 and some aluminum sulphate solution. Allow this to stand 

 and settle. It may require several hours. Compare the settling 

 in the first and second jars. Record your results in your note- 

 book. 



Now complete the following statements and write the 

 required paragraph. 



a. A solid, insoluble substance formed in a solution as a 

 result of chemical action is called a 



b. The precipitate was formed as a result of the chemi- 

 cal action between and 



c. The precipitate formed in part a of the experiment 

 was in color and (heavier, lighter) than water. 



d. The particles of the green precipitate were (larger, 



smaller) than the particles of the white precipitate 



formed in part b. 



e. The precipitate in part b was formed as a result of 

 the chemical action between and 



f. It was in color and (heavier, lighter) than 



water. 



g. Its particles were (large, small) 



h. Write a summary paragraph showing how the two 

 chemical actions studied above are used to aid the settling 

 of the suspended matter in water. Why is iron sulphate used 

 before the aluminum sulphate? 



READINGS WHICH WILL HELP ANSWER THE 

 PROBLEM QUESTIONS 



There are several ways of securing water. In rural 

 districts, in small towns, and in a few large cities, 

 wells driven into underground streams make up the 

 source of water supply. A lake may supply cities and 

 towns near it. Rivers and smaller streams, however, 

 make up the most important source of water supply 

 for cities and towns along them. It is often the case 

 that the location of a city determines the source of its 

 water supply. Cities away from rivers and in desert 

 country must resort to wells, while a city in the moun- 

 tains has lakes and streams formed by melting snows 

 for its supply. 



In rural districts and in most small towns, provid- 

 ing water is not such a tremendous problem as it is 

 in large cities, where water is often brought many 

 miles through pipes to supply the need. The following 

 table gives the average daily water consumption per 

 person in some of the larger cities of the country. 



CITY 



Chicago, 111. 

 Philadelphia, Pa. 



POPULATION 



(1930) 

 3,376,438 

 1,950,996 



GALLONS PER PER- 

 SON PER DAY 

 280 

 172 



