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It’s a fa­mil­iar sit­u­a­tion: you go camp­ing with friends, and you don’t have enough wa­ter. In this ex­per­i­ment, you’ll find out how to pu­ri­fy wa­ter from the near­est pond, You only need a plas­tic bot­tle, sand and a few burnt logs.

Safe­ty pre­cau­tions
Be sure to boil the wa­ter af­ter fil­tra­tion. Wa­ter may con­tain heavy met­als, so it is rec­om­mend­ed for util­i­ty pur­pos­es, and should only be drunk in ex­treme ne­ces­si­ty.

Reagents and equip­ment:
* char­coal (100 g);
* sand (300 g);
* plas­tic bot­tle with a lid;
* sta­tionery knife;
* cot­ton wool;
* awl.

Step-by-step in­struc­tions
Cut the bot­tom off the plas­tic bot­tle. Un­screw the lid of the bot­tle, make a hole in it with the awl and place cot­ton wool in the lid. Close the bot­tle and turn it up­side down. Place lay­ers of sand and char­coal in the bot­tle. The more lay­ers, the bet­ter the pu­rifi­ca­tion will be. The fil­ter is ready!

Pro­cess­es de­scrip­tion
Dirty wa­ter con­tains many or­gan­ic and min­er­al im­pu­ri­ties, and also var­i­ous in­sol­u­ble par­ti­cles of dust and earth. The sand pu­ri­fies the wa­ter of in­sol­u­ble par­ti­cles. Char­coal has good ad­sorp­tion and so ad­sorbs or­gan­ic and min­er­al im­pu­ri­ties. How­ev­er, this fil­ter has a con­sid­er­able draw­back: it does not pu­ri­fy the wa­ter from bac­te­ria and heavy met­als. So af­ter fil­tra­tion the wa­ter should be boiled well.

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