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Engineer, Brian Roffey

Engineer, Brian Roffey

Q: Why are my water costs so high?

BR: In the past many Caribbean islands relied on collected rainwater, stored in cisterns, for their everyday needs. As harmonious with nature as this sounds, the reality is expensive (because building and properly maintaining a cistern for potable water adds a large capital and operational cost) and not totally reliable. Today, the region’s modern water infrastructure plays a major role in making our tropical life possible.

On many island inhabitants fresh water is produced by desalinating water from the surrounding sea, primarily using a process called reverse osmosis (RO). In a nutshell, RO uses powerful pumps to push salt water through a semi-permeable membrane, forcing fresh water out the other side. With today’s technology, 40% of the salt water is converted to clean drinking water. Although the technology is ever improving in efficiency, a large amount of energy use is unavoidable. The principal energy source for RO plants is electricity, which, in turn, is predominantly produced by burning fossil fuels. As such, our water is produced indirectly from fossil fuels, the price of which fluctuates depending on the global market and local taxation policies.

In order to explore further, I’ve performed a basic analysis to estimate the amount of diesel used to produce a gallon of tap water in the Cayman Islands. In Grand Cayman, The Consolidated Water Co. (CWCO) and Cayman’s Water Authority (WAC) are responsible for producing and delivering the water we consume, and the Caribbean Utilities Co. Ltd. (CUC) provides the energy for its production. Please take statements below with a pinch of salt, as I’ve had to make a few assumptions based on the best of my knowledge.

  • The country’s eight RO plants are capable of producing approximately 10.2 million gallons of water per day. CWCO’s plants, servicing the Seven Mile Beach and the West Bay areas, have a capacity of 3.8 million gallons per day.
  • In 2013 CWCO sold over 750 million gallons of water, through retail operations, mostly to residences and businesses in the Seven Mile Beach and the West Bay areas.
  • In 2013 CWCO stated the direct cost of producing the water sold at about US$11 million. Assuming this is primarily for energy and the price of energy is US$0.33-0.35 per kWh, energy consumed can be estimated at 30 million kWh.
  • CUC produces energy at an approximate rate of 14.6 kWh per gallon of fuel.

Looking at these figures allows us to estimate that CWCO’s plants consumed 0.04 kWh for every gallon of water produced, which equates to about 0.0027 gallons of diesel.
Considering that a gallon of Fiji bottled water consumes a gallon of fossil fuel per every gallon delivered (and that’s before it ships from the USA), the drinking water produced locally is by far the cleaner option.

So drink up, but drink local.

1.    CWCO 2013 ANNUAL REPORT: http://ir.cwco.com/annuals.cfm
2.    CARIBBEAN UTILITIES COMPANY, LTD. 2013 ANNUAL REPORT: https://www.cuc-cayman.com/annual-reports
3.    PABLO CALCULATES THE TRUE COSTOF BOTTLED WATER: http://www.treehugger.com/clean-technology/pablo-calculates-the-true-cost-of-bottled-water.html
4.    http://en.wikipedia.org/wiki/Diesel_fuel

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