Tuesday, September 23, 2008

Water Scarcity

Ok, let's talk Water Scarcity.  

Rainwater Harvesting is a big deal here since there just isn't enough water to go around.  There are public utilities in some areas of the country but they hardly ever provide the quantity of water needed for the population they serve.  

We do have water piped in by the city utilities here in Narok.  However, we only get it pumped to us once a week...if we are lucky...and we never know how much they'll give us.  So...to solve our water scarcity problem...we have to turn to Rainwater Harvesting.  

The roof area of our little cottage is approximately 66.3 meters squared.  Our entire 66.3 meter squared roof is guttered and setup to run into two tanks.  We have a small tank hooked up to one half of our roof that can hold approximately 1.33 cubic meters.  The other half of our roof runs into a tank that can hold approximately 4.3 cubic meters.  We have approximately 5.63 cubic meters of Rainwater Harvesting capacity.


We have to make a few assumptions in order to run the formula....so we'll assume that Amanda and I each need 20 liters of water per day (that is the worldwide standard for human health...including consumption, bathing, dishes, etc.).  We'll also assume that the rainfall patterns in Narok will remain the same as it has for the last forty to fifty years...we are inputing rainfall data from between 1960 to 1979.  By making these assumptions, we can forecast how reliably we will have water in our Rainfall Harvesting tanks.  

By running the formula found here (http://www2.warwick.ac.uk/fac/sci/eng/research/dtu/rwh/model)we can get a rough estimate that we will reliably have water in our Rainwater Harvesting tanks approximately 64.8% of the time.  One thing we have learned is that the optimum cost to performance ratio for Rainwater Harvesting seems to be at about 67%.  We are close enough to that percentage that it probably isn't worth making any serious improvements to the system.  

We also crunched the numbers for a local college here in Narok.  The college has approximately 1914 square meters of Rainwater Harvesting area yet they have 891 square meters of potentially harvestable area.  They are currently at approximately 50% reliability.  If they finish guttering the buildings they can immediately jump up to approximately 65.8% reliability.  To finish guttering the buildings, they only need approximately 184 meters of gutter.  If they desired to go for the optimum cost to performance ratio, they could purchase another 20,000 liter tank and integrate that into their system.  That would bring them up to approximately 67% reliability.  As an example of how it just isn't worth it to go much higher than 67% reliability...if they wanted 80% reliability, they would have to purchase another 185,000 liters of storage capacity!  

Picture of a Rainwater Harvesting Tank

Rainwater Harvesting is so simple yet elegant.  Most houses already have guttering yet they lack the storage capacity to harvest the rainwater.  It is just so easy to add a bit of storage capacity to the end of your guttering line so that you have some spare water for your garden on those dry days...or like in our situation...it is used for so much more.  

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