Rain Water Harvesting - A Cost Analysis

Kids are very smart these days. When we showed a neighbor’s five year old daughter our water tanks, she asked “how much do they cost?” We told her the cost for each tank. She then asked “how much does water cost?” You know where she is going next even though she probably didn’t know herself! Here we have a five year old teaching us the concept of “return on/off investment!”  So, I will do a quick cost analysis to determine how long it takes to recover our investment.  9,000 gallons of water is equivalent to approximately 12 units of water charged by Mid-Peninsula Water District which costs about $5/unit in excess of 2 units. It would take us 30 years to recover our costs on the tanks alone. This is assuming that the cost of water will remain the same over the next 30 years which is highly unlikely.  By using the rain water, we are keeping the cost per unit from increasing to the next usage level. So, in reality, we would probably recover our costs a little quicker than 30 years. Based on our simple cost analysis, rain harvesting may not make sense; however, there are indirect benefits. For example, by harvesting the rain water, there is less water going into the ground and therefore decreases the amount of infiltration to the sewer system. This also decreases the burden on our storm drain systems during heavy rains. Who knows, during disastrous times, our harvested rain water reserve may become very valuable!  In reality, we didn't think too much about the cost as it's priceless the feeling we get knowing that we can be self-sufficient living off the grid like those who are using solar energy. :o) If you have a rain water harvesting system or grey water system, I would be interested to know what other benefits you have experienced.