How does desalination work?
The desalination process removes a portion of the freshwater from the seawater and then discharges the remaining saltier seawater back into the ocean utilizing mixing techniques that achieve neutral salinity within a few feet of the outfall. Eventually the freshwater that has been removed works its way back to the sea (through irrigation/drainage, wastewater discharge and general use), maintaining the natural balance.
Isn’t desalination really expensive and doesn’t it use a lot of energy?
Years ago desalination was very expensive and used a lot of energy. However, due to some great technological advances and industry standardization, the prices have come down significantly to the point where a city or individual in need of water can consider desalination as a viable option. (As an example, 8 years ago a RO membrane cost $5,000; today it is less than $1,000.)
Energy efficiency has also improved and we can currently produce 600 gallons of water for $1 of electricity. That’s 6 gallons for a penny using the current San Juan County electrical rate of 8 cents per kilowatt. At Watec, we continue to explore the field of desalination energy recapture to reduce the energy needed even further.
Won’t desalination make the sea saltier? What do you do with the brine?
No. All the freshwater extracted will eventually return to the sea through wastewater returns, irrigation/drainage and general use. The brine is returned to the oceans and mixes to neutral salinity within feet of the outfall discharge.
Why not just use rainwater catchment all the time?
Rainwater catchment is useful in some circumstances, but it requires a life style commitment if used as a primary freshwater source. It actually makes more economic sense and utility if used as a supplement for landscaping. Also, on a per gallon cost basis, rainwater catchment far exceeds the cost of desalinated water.
It is also tempting to think that rainwater catchment has no environmental impact. However, just like historic freshwater resources, it diverts freshwater from the natural aquatic environment harming these sensitive wetland zones.
Can you really drink recycled wastewater?
The only obstacle to drinking recycled wastewater is an aversion to the idea. It is 100% safe and of good quality. It is estimated in London that every drop of water has been used by humans 7 times before being discharged into the sea. A lot of great research and implementation has been done on this topic. See the Orange County, California, Groundwater Replenishment Program for more on potable water reuse.
For many however, drinking recycled wastewater is too large of a psychological leap and they prefer to limit their use of recycled water for irrigation. Water reuse and recycling in the form of irrigation is a viable option even for individual homeowners.
If everyone used desalination, wouldn’t that be harmful to the environment?
On the contrary, it would actually lessen our impact on the natural environment by replenishing the freshwater we now divert (and steal). This would enable us to recharge our aquifers, replenish our wetlands and generally allow freshwater to exist for aquatic life which has suffered under the current water resource conditions.
Aren’t harmful chemicals used in desalination and discharged into the environment?
No chemicals are used in the desalination process; we only use ultraviolet light and naturally existing ozone from the air for disinfection. The only chemical to be seen in our utility rooms is chlorine. Chlorine in drinking water is mandated by the state department of health in all class “A” potable water systems and is used as a water system distribution disinfectant.