1. A nonchemical turbidity removal layer in a slow sand filter
2. Region in earth (soil) above the water table
3. Compound associated with photochemical reaction
4. Oxygen used in water that is rich in inorganic matter
5. A stream that receives water from the zone of saturation
6. The addition of water into a groundwater system
7. The natural water cycle
8. Present in intestinal tracts and feces of animals and humans
9. Discharge from a factory or municipal sewage treatment plant
10. Common to fixed-film treatment devices
11. Identified water that is safe to drink
12. The capacity of soil to hold water
13. Used to measure acidity and alkalinity
14. Rain mixed with sulfur oxides
15. Enrichment of water bodies by nutrients
16. A solution of known strength of concentration
17. Water lost by foliage
18. Another name for a wastewater pumping station
19. Plants and animals indigenous to an area
20. The amount of oxygen dissolved in water