Step-by-step Instructions to build a working model
Contributed by Vasudevan Srisailan 
Hydro electric power generator
Contributed by Eva Johnson.
Water level indicator and alarm
Contributed by Electronics For You
Following working models are courtesy - Arvind Gupta Toys
Make a pump with just an old bottle and some cello tape.
Try making this with a small variation. A coin does the trick.
Modifications of this simple pump is still used in parts of Andhra Pradesh to lift water.
An extension of the previous pump
With an ordinary plastic straw, broom stick, cello tape and scissors
you could make a real centrifuge in a jiffy.
One minute film on how to make this
Make a water pump using a film can, bottle cap, coin, cycle spoke and other trinkets
This pumpis like the one used to draw water from a well
Try a variation and use a syringe instead of a film can
This pump can be used to lift large quantities of water
Finished with a toothpaste tube? Not just yet. Try out this pump instead of throwing the tube in the dustbin
A couple of straws, some beads and ball bearings is all you will need to make this pump
Using an old pen body as cylinder, thread wrapped bicycle spoke as piston and a cycle ball bearing as a valve you can make a very workable pump
Use a straw instead of the pen body
You can make a simple force pump using two plastic syringes and other common things
Understand the working of a hand pump
Designed by V C Kandkur, understand the principle of hydraulic pressure and make this JCB truck
This experiment shows you how a submarine works. Jazz up the bottle to make it look like a real submarine
Make this turbine first
Try the hydroelectric power generator model detailed on this site