How Does Water Recycling Work and Why is Water Recycling Important?

Water reclamation and recycling is increasingly an essential element in the sustainability plans of many cities. It makes sense. By recycling water—particularly for irrigation and industrial uses—we can reduce the demand for water sourced for drinking water. But how is water reused? And how does water recycling work? As you can read below, there are different processes used to produce different types of water.
How is Recycled Water Treated?

SUEZ uses different methods to prepare wastewater for reclamation, depending on its intended use. For example, water that will be used for irrigation needs to be treated differently than water that will be used in industrial high-pressure boilers.


  • Irrigation water for large turf areas, like golf courses and parks: First, solids are removed from wastewater. Then microorganisms—beneficial bacteria, protozoa, metazoa, algae and fungi—are added to the wastewater where they feed on waste particles that are too small to see or too light to settle to the bottom of collection tanks. Bacteria clump together forming masses, called floc, that settle and separate from wastewater liquids. This settled mass is called sludge. The remaining water goes through a filtration process where the water percolates through layers of fine anthracite coal, sand and gravel. In addition, disinfectants, such as chlorine, are added to kill germs or treated with ultraviolet (UV) light. At this point, the water is ready for use in landscape irrigation and various industrial and commercial uses.

  • Cooling tower water for office buildings and manufacturers: In addition to the steps listed above, the wastewater is processed to remove ammonia.

  • Seawater barrier and groundwater replenishment water: Wastewater is filtered by microfiltration and reverse osmosis membranes and disinfected for use in maintaining a barrier against seawater intrusion and augmenting local well water supplies. In microfiltration, water is pressurized through pipes containing straw-like fibers with pores that are 5,000 times smaller than a pinhole. In reverse osmosis, water is pressurized at about 200 pounds per square inch through tightly wound layers of membranes with pores that are 5 million times smaller than a pinhole.

  • Low-pressure boiler feed water for refineries: Wastewater is filtered by microfiltration and reverse osmosis membranes, as described above, for use as low pressure boiler feed water.

  • High-pressure boiler feed water: Wastewater is filtered by microfiltration and reverse osmosis membranes—twice—for use as feed water for high-pressure boilers.

Why is Water Recycling Important?

Although 75 percent of the earth is covered by water, only 1 percent of that is freshwater available for serving the water needs of more than 7.8 billion people in the world today. Because of drought and pollution, that 1 percent is dwindling. To make matters worse, the world population continues to grow, further increasing the demand for water. In many areas, water must be imported from outside the region.

Recycling Water Conserves Resources

As the available water supply is decreasing, the demand for water is increasing. To ensure that we have enough water to meet our present and future needs, we need to conserve water and expand the use of recycled water. In essence, by expanding the use of recycled water, we are actually helping to conserve our drinking water supplies.
There’s also an added big bonus. Recycled water is good for the environment. Without recycling, secondary treated, nitrogen-rich sewage water would be discharged directly into our oceans—affecting the marine life. By recycling, less water is discharged, improving the environmental condition of our coastal waters.

What Can Recycled Water Be Used For?


  • Irrigation water for common greens: large turf areas, like golf courses and parks. Reclaimed water can be used for many other non-potable uses, as well, such as washing down equipment and tanks; dust control or surface cleaning of roads, construction sites, and other trafficked areas; concrete mixing and other construction processes; and indoor uses, such as flushing toilets.

  • Low-pressure boiler feed: Recycled water is used for generating steam to be used within the refining process. Additional treatment steps, including microfiltration and reverse osmosis are utilized to reduce the total dissolved solids and other inorganic constituents such as total hardness and silica, to levels acceptable for steam generation.

  • High-pressure boiler feed: This water, used by refineries and other industries, is produced in much the same way that low-pressure feed water is, but in this instance the low-pressure boiler feed output is treated with a second pass of reverse osmosis. The low-pressure boiler feed treatment system reduces the total dissolved solids in the recycled water to approximately 35 mg/l, whereas the high-pressure boiler feed treatment system reduces the total dissolved solids ever further, to approximately 3 mg/l.\

  • Seawater barrier: To prevent seawater intrusion, a seawater barrier was constructed. A seawater barrier is a series of injection wells positioned like a dam between the ocean and the groundwater aquifer. These wells inject water along the barrier to ensure that the water level near the ocean stays high enough to keep the seawater from seeping into the aquifer.

  • Recharging aquifers: If wastewater is properly treated, it can be used to recharge inland and coastal aquifers and municipal water wells.

Is Recycled Water Safe to Drink?

Reclaimed and recycled water is not typically used directly for drinking water. However, SUEZ can treat water to the point where it can be injected underground to augment groundwater supplies used for drinking water. SUEZ’s LEAP*mbr (membrane bioreactor) technology is used in the process. At its core, the LEAPmbr uses the ZeeWeed membrane, an advanced ultrafiltration technology that separates solids, bacteria and viruses from water or wastewater.

MBR effluent is then further treated using reverse osmosis membranes and an advanced oxidation process before being injected into the aquifer.

In September 2019, the City of Morro Bay Water Reclamation Facility Project in central California partnered with SUEZ to adopt this process to make recycled water safe to drink. Though there are more than 50 operating MBR projects in California that produce recycled water for irrigation and industrial use, when permitted, the City of Morro’s facility will be the first to use MBR technology in a process to recycle wastewater to augment groundwater supplies used for drinking water.
Learn More About Water Reuse
If you want to know more about how water is reused and how water recycling works, we’re more than happy to answer your questions. SUEZ has decades of experience and dozens of case studies from around the world we can share with you.

Contact a representative to inquire about SUEZ’ water recycling services or learn more about wastewater reuse here.