Water Purification

2. Negative ions are called anions. What are positive ions called?
4. This word means safe to drink
6. The process in which screens remove large particles as water enters treatment plant
7. The percent of the earth's water that is fresh water in lakes and rivers
9. A contaminant that can cause algal blooms
10. The quantity of oxygen used by bacteria over five days at 20 degrees Celsius
12. The third category of contamination in addition to biological and physical
16. This industry produces tetrachloroethylene
18. Keeps chlorine dissolved in water longer for its trip through pipes
19. An underground water source
20. An alternate disinfectant
21. The most important step in water purification
22. This stage of wastewater treatment involves aeration and chlorination
23. This type of light can be used to disinfect water.
24. Leaks into lakes from boats or sea-doos

1. Sand & carbon filters bacteria, chemicals & floc
3. Water is "softer" when ions of magnesium and this element are removed
5. The type of bacteria that caused the water contamination in Walkerton in 2000
6. Chemicals that cause small particles to clump together
8. This heavy metal leaches into groundwater from landfill sites
11. This cycle provides us with fresh water
13. Air pumped into water during this process reduces taste and colour problems
14. Reduces tooth decay when added to water
15. Clump of a jelly-like precipitate.
17. Floc sinks to the bottom of tank as water clears
18. Canadian drinking water is only allowed to have 0.025 ppm of this substance.