Although untreated household waste water poses a health risk to people, find out whether gray water can irrigate plants without placing humans in danger. Students can conduct a simple, long-term experiment by collecting water from a household septic tank or disconnecting pipes from sinks in the house and setting a bowl or basin under the disconnected point to catch wastewater. Buy two identical plants and place near each other so they receive the same oxygen and sunlight exposure. Water one using 1/4 cup of distilled water daily and the other with 1/4 cup of gray water for eight weeks. Record plant height measurements, number and color of leaves produced and the appearance of any fruit or flowers to determine whether wastewater is effective for irrigating plants.
For centuries, farmers considered heavy rains during several critical times of year essential to the growth and development plant. This belief influenced the development of overhead and lateral-move (device moved from row to row) irrigation systems used on American farms for many years. Farmers in desert regions of the world who can't depend on rain and lack plentiful reservoirs of water developed a drip-irrigation system that uses a fraction of the water distributed by sprinklers, but produces edible crops. Compare which system is more effective by setting bell peppers underneath an overhead sprinkler system and a drip system. Record how much fruit is produced by each plant and measure their diameters. Report on the benefits and disadvantages of each system and draw graphs to compare.
Prepare three salinity concentrations in spray bottles by combining one part distilled water with three parts ocean water in one bottle, three parts of distilled water to one part ocean water in the second container and equal parts of distilled water and ocean water in the final bottle. Water identical plants daily with 10 sprays from each salinity concentration. Observe and record plant growth over a six-week period to determine whether ocean water can be incorporated into an irrigation system to conserve freshwater.
Determine whether adding oil to the soil will help retain underground water without hurting vegetation. Fill three large plastic tubs with soil and plant three identical vegetable-producing plants. Place both tubs under heat lamps and use a hair dryer to blow hot air at the plants daily for 10 minutes to simulate an arid environment. Water the first tub with distilled water daily. Water the plants in the second tub and apply cooking spray over the soil surface. Water the plants in the third tub and pour a stream of vegetable oil around the base of each plant. Test the water retention of each tub and observe plant growth through height measurement and heat production.