Desalination makes sense as an alternative source – to a point.
In the next 10 years, the increase in population in the U.S and worldwide is going to be dramatic. Where are we going to find water for all the people and still have water left over for landscape irrigation?
World population today is more than 7 billion people, and in the next 10 years the United Nations estimates we will add another billion. About 71percent of the earth is covered by oceans. Removing salt from water, especially ocean water in coastal communities, is an option for solving the problem of finding more water for the increase in population.
Desalination or “desal” is the process used to remove salt and minerals from seawater or brackish water. According to Planet Green, the first and only 24-hour eco-lifestyle television network, there are more than 15,000 desal plants operating in the world, and more than 300 of those are located in the United States. About half of them are in Florida. Texas and California combined have another 86.
How does it work?
There are two popular technologies currently used for the desalination process. One is membrane technology. This process uses pressure to force water through a membrane that does not allow the salt particles to pass through. You probably know this process by the term reverse osmosis. Sometimes, instead of using pressure to drive the water through the membrane, electricity is used and we call this a voltage-driven process.
A thermal process is when salt water is heated which produces vapor and then is condensed and collected as fresh water. This is very similar to the evaporation process of ocean water and explains why rain water is not salty. When the ocean is heated by the sun, the water evaporates and escapes as vapor. The salt does not evaporate and is left behind.
Benefits of desalination.
Ninety-seven percent of the world’s water is salt water. Desalination of salt water provides an unlimited supply of water to the world’s population. As demand for water grows, desalination provides a source of water that can meet our new demands for water.
The costs for desalination are trending lower, according to the WateReuse Association. And the quality of the water is very high, according to Carlsbad Desalination Project, which consisted of more than 1,200 decision-makers and stakeholders touring the pilot plant and sampling the product. More than 99 percent of respondents rated the desalinated water taste as either “excellent” or “good,”with 83.9 percent ranking it as excellent.
Combining this with the availability for water makes desalination attractive to many people around the world. The main issue around the cost of desalination is the energy needed for the process of removing salt and then moving the water.
The good news is that in the U.S. 53 percent of the population lives within 50 miles of the coastline. This keeps the cost reasonable compared to places like Riyadh, Saudi Arabia, where almost all the domestic water used is produced at a desalinization plant at the gulf and pumped more than 400 kilometers.
As the price of traditional water sources increase and the efficiencies of desalination improve, some believe in the near future desal water will be less expensive than traditional sources of water.
After twelve years of planning and more than six years in the state’s permitting process, the Carlsbad $1 billion desalination project has received final approvals. The San Diego Water Authority has contracted with the plant to purchase all the water it produces. It will be piped from the coast (where the desal process will take place) to San Diego's aqueduct in San Marcos 10 miles away. The plant is a reverse osmosis plant and should be producing water by 2016. By the year 2020, because of improved efficiencies and high cost of water, the desal water should be less expensive than the municipal water.
So what's the problem?
The first challenge is the cost of the water produced. As mentioned above, the cost is decreasing overall, but even in coastal communities we find the cost of desal water to be about twice the cost of traditional water.
Another expense is the cost of energy needed to operate a desalination plant. According to a congressional research service report, approximately 33-50 percent of the operating costs of a desalination plant are for electricity. This energy consumption also adds to greenhouse gas emissions, which in turn threaten our coasts.
In addition to costs, what we do with the brine created in the desal process is a big question. If the concentrated salt water is disposed back into the ocean, there is chance the salt will sink to the bottom and may have an adverse effect on marine organisms.
There is also a concern the apparent ease of desalination will decrease the motivation for conservation and the development of additional ways to save water. This might be the biggest issue of all since we know we can’t afford to slow conservation efforts.
Another negative we don’t hear much about is the impact of the water on infrastructure. Pure desal water is highly acidic and is harmful to water pipes so it has to be mixed with other sources of water that are piped onsite or else adjusted for pH, hardness and alkalinity before being piped offsite.
A combined approach.
I believe the biggest issue today is capacity. When it comes online in 2016, the $1 billion Carlsbad, Calif. plant will produce 50 million gallons of drinking water per day. That is enough drinking water for about 300,000 San Diego residents annually. San Diego County currently has more than 3 million residents. To supply desal water to all of them would require a tenfold increase in desalination plants.
There is also a concern about developing complex and expensive means of water when simple and cheaper opportunities still exist. Conservation has to be given a chance to work. Incentives from water agencies in forms of rebates for better technology like smart irrigation controllers and high efficiency nozzles can make a positive impact on landscape water use.
I believe the solution to our water issue is going to be a combined approach of conservation, technology and desalination. In coastal areas and inland area with access to saline groundwater, desalination has to become more prevalent. We're seeing proof of success in cost reductions for desal and environmental impacts from the brine in the discharge water have been significantly reduced in Australia.
As desal technologies continue to develop, and energy use continues to fall, costs are reduced and the viability of desalination improves. At the same time, additional emphasis needs to be placed on infrastructure, catchment, technology and conservation.
We can make an impact on water availability with a combined focus approach. This type of approach is going to be needed to make water available to everyone and their landscapes.
The author is director, water management solutions at ValleyCrest Landscape Co.