What it shows
Open ponds and tanks lose a lot of water by evaporation in summer. Testing four covers on trays of water shows which method saves the most water.
The science
Water evaporates from the surface, faster when the sun is strong, the air is dry and the wind blows. A shade lowers the sunlight and wind on the surface, floating balls cover part of the surface, and an oil film blocks the surface but can harm life. The tray that loses the least has the best cover.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Five identical shallow trays or basins
- Foil or a cloth shade
- Table tennis balls or small floating balls
- A few drops of cooking oil
- A measuring cup or syringe
- A ruler to read water depth
- A sunny, safe spot
Safety
For this project: Do not pour oil into drains or natural waters. An adult must clean up oily water. Keep trays out of reach of small children and pets.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Pour exactly 500 ml of water into each of five trays.
Leave tray 1 open as the control.
Cover tray 2 with a cloth shade held above it on sticks.
Fill tray 3 with a single layer of floating balls.
Add a thin oil film to tray 4 using a few drops.
Cover tray 5 completely with foil, leaving a small air gap.
Measure the remaining water or depth each day at the same time for a week.
Plot water lost against days and compare the covers.
What you should see
The control loses water fastest, and the covered trays lose less. The graph shows the saving of each method.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What affects evaporation?
Sun, wind, dryness of air and surface area.
2Why not use oil on a real pond?
It harms plants and animals.
3What do real tanks use?
Shade nets, floating covers and trees.
4Why have a control tray?
To compare with no cover.
Take it further
Repeat on a windy and a calm day and see how wind changes the loss.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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