In normal house hold water supplies, most of the cost of water purification rises because of the ultra violet technology used in water purification.

The attached image explains the concept.

Water lens: Simply take a cellophane sheet, and put water on it. Water will bend the sheet, and take a parabolic shape of a lens on its own! Using the basic optics principles, the focal point of this water lens can be easily calculated to be within 2-5 m.

Idea is simple. Make a water tank. Put water lens on top of it. Concentrate all of the solar radiations, including UV radiations, at one point, inside the water tank, heat the water and in the process make it extremely pure for drinking (According to a Brown University research, it kills 99.99% of all pathogens, including VIRUSES.

USP: merely heating the water in solar heater may kill some pathogens, but don't kill viruses. We use glass made transparent tank, and treat the water with concentrated UV radiations, and kill all of the viruses too. No moving parts in whole arrangement, hence almost zero maintenance cost in normal operation. No external energy input, totally self sustaining unit based on solar radiations.

Outside container is a cylindrical tank made of copper galvanized with zinc. Inside there is a step arrangement made of glass. (Steps increases the exposed surface area and hence all of the water is heated uniformly). On the top is water lens. On top of it the tank is a ceiling of green house glass to ensure that the heat is trapped inside the tank for ever, and extremely large temperatures can be reached. (just like cars)
The focal point of the lens is at the bottom of the steps, this means, bottom water will be heated much quicker, become less dense, and then travel upwards to ensure uniformity of heating (Just like as it happens when you boil water).
On top of the bottom steps (marked in red) are two bimetallic strips which bend at around 99 C. Idea is...when the whole water is heated to a temperature close to 99, the strips will bend and open up the opening and purified water will rush out of the tank.
The focal point close to exit ensures that
1. water has enough UV exposure
2. water is heated to largest possible temperature--right before exiting that all pathogens are killed.

We need a hand pump, to bring the water to surface. Another advantage of this system is USER-INTERFACE--rural people are habitual of drawing water from hand-pumps, and hence this arrangement will work perfectly fine. Also, who will fill water in the tank?! Everyone is lethargic. So the design of the hand-pump itself is modified. Through the same rod are connected two pistons--one connects water tank to surface exit, and other connects ground water line to input of purifying tank. So when one draws water out of tank, one puts back an absolutely equal amount of water into tank without one`s knowledge.