Indirect Potable Reuse: The Solution to Future Water Shortages

           know_your_h2o_logoClimate change poses an immediate and severe threat to freshwater sources. By mid-century, annual average river runoff and water availability are projected to decrease by ten to thirty percent over some dry regions at mid-latitudes, which spells trouble for the southwestern United States. Water supply, sanitation, agriculture, and human health all depend on a stable and adequate freshwater supply. The Colorado River, which is the primary water supply of many western states, is already currently overdrawn, and the Ogallala Aquifer, which underlies portions of Kansas, Texas, Nebraska, Oklahoma, Colorado, Wyoming, and New Mexico, supplies thirty percent of the United States’ irrigation water, is expected to experience severe depletions by 2020, leading to a fifty percent reduction in irrigation on the high plains of Texas by 2050.

Recycle for clean water

Possibly the best solution to combat the effects of climate change is the process of recycling wastewater for potable use. Wastewater recycling practices are widely use today; however, the water is most commonly treated to levels that are satisfactory for irrigation, and not to the high standards required for drinking water.

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There are two methods for recycling effluent: the first is known as Direct Potable Reuse (DPR) and the second is Indirect Potable Reuse (IPR). DPR involves collecting effluent, treating the effluent to the standards required by the Clean Water Act before the effluent is normally discharged into a water source, further treating the effluent with advanced treatment processes so that the effluent meets potable water standards, and finally pumping the advanced-treated effluent directly back into the potable distribution system.  IPR, on the other hand, adds an additional step. After the effluent has undergone all the above-mentioned treatment processes, the effluent is added to a potable water supply, such as a reservoir or groundwater aquifer. While in the reservoir or aquifer, the water is able to undergo natural filtration.

Compared to DPR, IPR may seem inefficient and unnecessarily more expensive, due to the excess pipes required to bring the water to the reservoir or aquifer, a cost that is not needed under DPR.

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 However, IPR gained public favor due to the ‘ick factor’ associated with DPR. For example, when the concept of DPR was first introduced in San Diego, the nickname “toilet to tap” quickly surfaced, and the public responded negatively. This nickname has since been applied to IPR as well, although it is inaccurate to those who understand the IPR process.

There are numerous advantages associated with IPR. Possibly the most attractive advantage, and what makes the process so unique, is that IPR allows the supply of potable water to increase with population size.

When an areas population increases, the amount of wastewater generated also increases. The more wastewater that is generated, the more water is available for recycling using the IPR system. IPR therefore has the potential to provide a stable, constant source of potable water in the face of droughts or contamination.

Another advantage of IPR is that it prevents overdrawing of aquifers, rivers, lakes, and other water sources. In areas where groundwater is the primary source of potable water, IPR has the potential to reduce costs associated with groundwater overdraft, such as preventing the collapse of land overlying groundwater aquifers, adding pumping lifts, and preventing the increased salinity of groundwater resources that results from overdrawing.

The benefits of IPR extend to the environment surrounding areas implementing the technology, and beyond. If used as the primary source of potable water, IPR will decrease the diversion of water from sensitive ecosystems, thus preventing the deterioration of water quality and ecosystem health by reducing and preventing pollution.

The most notable disadvantage of IPR is the cost of implementation. The necessary infrastructure includes a reservoir or aquifer of adequate size, pipes to transfer the treated effluent to each treatment facility and the reservoir, and finally, the advanced treatment facility itself.

Overall, the advantages of IPR far outweigh the disadvantages. Furthermore, not implementing IPR leaves our country vulnerable to the inevitable health effects associated with the rapidly decreasing amounts of freshwater as a result of climate change.

 

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