Concerns and Facts on Indirect Potable Reuse/Toilet-to-Tap
“Sewage Recycling” “Toilet-to-Tap” “Reservoir Augmentation” “Indirect Potable Reuse” etc. etc. etc.
The names for this process go on ad nauseam and reflect San Diego’s split on the subject, but the truth is that there are many concerns that need to be addressed from a factual stand point.
Concern 1: This seems kind of gross. What if the purified water has left over sewer-grossness in it?
Fact 1: Purified sewage water is cleaner than what comes out of your tap today.
Many San Diegans express concerns over the health, safety, and cleanliness of recycled sewer water but that fear is misplaced. In 2008 a study was done by the Environmental Working Group showed that out of 46 major cities around the country San Diego tap water was ranked the 5th worst. Los Angeles, where San Diego purchases their water from, was THE worst. Rankings were based on a database of national tap water quality gathered from state water offices. For more information check out this site.
The truth is, all water is recycled sewer water. The water which we import from the Colorado River and other sources has trace amounts of pharmaceutical drugs. How you ask? When we take drugs our body doesn’t fully process them so they pass through into the sewer system. The sewer water is then not treated for those drugs and is used in irrigation. The irrigation water goes through the water cycle and comes back down into the Colorado River still carrying those trace amounts of pharmaceutical drugs. The water is then pumped and sold to us at outrageous costs.
However, the process used for purifying sewer water does remove pharmaceuticals! (As well as other bad stuff, even as microscopic as bacteria and viruses.) The process used for purifying sewer water is known as reverse osmosis and is so extensive in its ability to purify that the water we purify from the sewer will be even cleaner than the gunk we get now.
The current process for sewer water looks like this:
- The first step is a filtration process where they pull out all the solids.
- Then it is used for irrigation.
The process for purifying the water looks like this:
- Filter out the solids
- Pass through teeny-tiny microscopic fibers to pull out bacteria and viruses
- Pass through membranes with holes so teeny-tiny that only the water molecule will get through
- Add hydrogen peroxide and zap with ultraviolet light to disinfect, not necessary but done just in case
The reverse osmosis process can be used to filter any quality water and is currently used to filter sea water (desalination). For more on where this information was obtained check out this article.
Do a taste test. Find a water store using reverse osmosis and compare a glass of that to a glass from your tap. It makes no difference what the quality of the water was when it went in because this process filters it all out. So when you realize the difference, remember it’s the amazing process of reverse osmosis that makes it all happen.
If you’re wondering why we don’t just use this process for sea water instead of sewer water, you are not alone but read on and you’ll understand.
Concern 2: This sounds too costly. Why don’t we just stick to desalination?
Fact 2: Using reverse osmosis on sewage water is more cost effective than desalination.
In 2010 a study was done by the Equinox Center analyzing the marginal costs and energy intensity of water alternatives. (In layman’s terms: How much money and energy this is going to take) The study showed that on the high end, desalination’s marginal cost would be $2,800 per acre foot while recycled potable water would be $1,800 per acre foot. This is because the energy intensity for desalination is more than twice as high as for sewer water purification. It also helps that the recycled potable water only has additional treatment costs and there won’t be any additional costs for a new water distribution system, whereas desal requires a whole new plant to suck out the sea water.
The study also states that of all the water alternatives, (including imported water, surface water, ground water, and conservation) desalination is the highest cost option. For more on this study, click here.
So the question is, if science shows that we will get the same water through reverse osmosis regardless of whether it starts as sea water or sewer water, why would we pay more to get the same thing?
Concern 3: It still seems like a lot of work. Can’t we just stick to what we’re doing?
Fact 3: San Diego is in need of more drinkable water and relying on imported water is causing significant rate increases without an end in sight.
San Diego is a semi-arid region that uses water like it’s the tropics. According to the Equinox Study the direct water resources San Diego has (such as surface water, ground water, and conservation) “do not have the capacity to serve as major sources for San Diego County’s water requirements.”
While rates may increase with the development of indirect potable reuse or with desalination, at least the money we spend is going to our own resources, thus ensuring our water independence and a future decrease in rates once the project is up.
The current water rate increases we have been seeing and the future rate increases we are going to see in the near future are only going toward Metropolitan Water District in Los Angeles. Water is the sources of life and we cannot let someone else dictate our rates and rations. At least with this new San Diego water source we will have an end in sight as we will no longer have to purchase water and the costs of developing the purification system are only temporary.
In summary, we can see that our options for major water resources are:
- Use reverse osmosis and pay a little (IPR),
- Use reverse osmosis and pay a lot (Desal),
- Continue purchasing bad water at high prices and be subject to total reliance on someone else’s pricing scale (Importation), or
- Run out of water (Groundwater, Surface Water, Conservation).
What is your choice?