Integrated stirling water pumping
Use stirling pumping principle, construction with easy to find materials and a lot of functionality.

Solution

General concept: The best way to utilize the energy of the environment is always to take on account the sun, the air, the water and gravity. The system I designed uses the heat of the sun to increase the pressure of the air in a glass taped box (the box is painted in black to absorb more heat).  The expansion of the air makes a piston to move, which makes a flywheel to rotate, and this moves another piston that goes directly into a postive displacement reciprocating pump, this pumps  a flow of water that goes directly into a metallic piping system that is inside the air box, and this forces the air to absob the coolness of the water (this is why this piping should be metallic, to allow a fast heat transfer), and the air contracts, making the piston to move again. The movement of the flywheel maintains a flow, you just have to give it a boost at first. The idea was to find an alternative to the anormous pistons that stirling engines can have, to economize material and make it easier to replace parts.

The wheels: The flywheel is a combination of two bicycle wheels, this gives it weight enough to function. When you use the pump you have them together, and when you have to traslade the product, you disconnect the pump and put the second wheel back to it's place.

The solar tracking system is pasive, it consists of tho little boxes just as the big one, but in this case, one in one extreme of the big box and one in the other. When a little box gets more heat than the other, it will make the other extreme to expand and viceversa, so if the two extremes are getting the same amount of heat,  the big box will stay perpendicular to the floor (at noon).

Variabilities: the system is designed to be modular, you can add another box with it's own structure (you join the four wheels together so they have more weight), and you connect the boxes with two tubes to allow the air to pass. This will double the speed of the pumping.

The outer wheel (while in use) has a sprocket to connect it to a bicycle or just some pedals that the family could have form past pumps or similar. This is a response to the "no sun no water fear", so it gets into a "no sun = make some exercise"

The vast space underneath the big box can be used to put a small pool. This is for when the farmers may use the system to generate electricity: the pool has water that is right beneath the system, and so it works faster, it can have an excedent of energy and it can be harnessed and converted into electricicty. Of course while doing this you can't pump water at the sime time.

This three aspects of versatility allows for some marketing proposals, such as packages: the basic, the double, the emergency package, etc.

Viability: The system is estimated to cost about 600 dollars, but there is still some research to make about this, it can vary, but one thing is sure: the parts are vary easy to repair due to the coupling with bikes and pumps.