Zero-energy, natural water filtration unit

All of the irrigation in the farm uses the water from the lake, however, we did have a borewell for drinking water. Even though that is <1% of our total water consumption, we always wanted to break that last connection to consuming borewell water. As luck would have it, the borewell motor broke down. Despite spending more than a lakh to get it working, we failed to repair it. The combination of running a single-phase motor, on a solar-battery-inverter combination, and a borewell that had a lot of silt – led to wasted, time, money and effort (that itself deserves another post). Anyway… this post focuses on how we built a zero-energy, fully natural, filtration unit for getting potable water from the lake.

This consists of 4 stages:

First Stage: Filter heavy sediments. Water is pushed up from the bottom of a tank that has rocks. Big rocks at the bottom, medium rocks and medium pebbles in the centre and finally small pebbles at the very top. Since the water enters from the bottom, the sediments are caught as the water moves up and on the very top, the water has only fine sediments left. This water from there flows into the top of the second stage.

Second Stage: Filter fine sediment: The second stage comprises of medium and small pebbles at the bottom, coarse sand in the middle and very fine sand on the top. As the water from the first stage falls at the top and percolates down, all the fine sediments get filtered and clean water starts to drip to the bottom. This clear water is then sent to the top of third stage.

Third Stage: Filter chemical impurities: The third stage comprises of almost similar layers as the previous stage, but has a big layer of activated charcoal at the top. As water again percolates down from the top, it gets further cleaned as well as all the chemical impurities are captured by the activated charcoal. At this point, the water is almost potable. This water is sent to the fourth stage.

Fourth Stage: Kill the biological impurities: The water from the prior stage is stored in a tank that is painted black and has copper plates suspended inside it. The heat from the Sun is used to kill the pathogens and the copper is a known germ-killer. The combination gives us clean potable water!