Did You Know Rainstorms Change the Water Treatment Process?

For most people, rain in the forecast is usually little more than a mild inconvenience. But at LCA, we have to watch that forecast very carefully, because rain affects how we treat and supply your water. We need to know how much we are getting, when it’s supposed to arrive, how long it should last, and if there is more rain coming after the initial storm passes.

You might be thinking, “But it’s just more water. That’s a good thing, right?”

An illustration showing a typical water treatment cycle, for a post on storm preparation. .
An illustration of a typical water treatment cycle.

Well, yes … and no. While rain replenishes ground water, heavy or prolonged periods of rain have a big impact on water quality. That’s because rain washes contaminants into source water — everything from leaves and eroded soil to litter such as plastic bags, bottles and cans, and sometimes even larger objects like lawn chairs and tree branches.

The increased level of contaminants brought by runoff makes the water more difficult — and much more expensive — to treat. So, when forecasters say we’re getting a lot of rain, we need to make preparations. That’s been especially true over the past year, which a Morning Call story points out has been the third-wettest on record.

How Your Water is Treated

To understand why we need to prepare, it helps to know how the treatment process works. We’ll use LCA’s Allentown Division as an example.

The average daily demand for Allentown is about 22 million gallons per day. We can usually satisfy about half of that demand by using groundwater from two different sources: Schantz Spring and Crystal Spring. The remaining water must come from either the Little Lehigh Creek or the Lehigh River. We generally use the Little Lehigh.  

At the beginning of the treatment process, we must screen out any large debris. This is done with a coarse screen made up of bars spaced 2.5” apart. It captures big items such as sticks, trash and leaves. Our workers clean the screen manually, which can be a very physical process  — especially during the fall months with all the leaves! 

Next in line is a finer screen, which removes many of the smaller things that get past the coarse screen. Still, some smaller debris get through and can clog up water pumps and sample lines. Also, the finer screen doesn’t remove any of the “dirt” in the water, which makes it cloudy (the technical term is “turbid”).

Now the true treatment process begins. We add a substance to the water called a coagulant. In baking, a good example of a coagulant is an egg — it acts to bind together other ingredients.

In the water, our coagulant causes the dirt particles to bind together so that we can remove them in a process called “settling.” This begins the disinfection process. These particles form into a solid, which we dispose of after it’s collected in big batches. The higher the cloudiness, or turbidity, the more coagulant must be used (and the more solids are produced).

 At this point, we also add chlorine (like the type used in a pool) to eliminate things like bacteria. The more “dirt” that is in the water, the more chlorine is needed for proper disinfection.

Finally, the water is filtered to capture any microscopic particles that weren’t removed in the settling process.

The treated water is then stored in what we call “finished water” reservoirs. Our Allentown division uses three: One holds 30 million gallons; the other two hold 10, for a total of 50 million gallons of water. Each feeds a different section of the city.    

In theory, if the reservoirs are full and we’re not adding more to them, Allentown could make it over two full days without running out of water. However, due to the hydraulics of the system (the majority of our infrastructure operates through gravity) it is impossible to fill all the reservoirs to the brim. And they may not empty at the same rate, either. Depending on circumstances including water usage in different parts of the city, one area could run out of water before the others.

During normal weather, we treat water and fill our reservoirs over a period of three to five days. Once they’re full, we turn off the incoming water for 24-48 hours. This allows the reservoirs to drain down a bit through our customers’ regular usage. When they’ve been sufficiently lowered, we start the cycle all over again. This ensures a constant supply of clean water — if it sat in the reservoirs for too long, it would require more treatment.

Storm Preparation

When we know there’s a storm coming, one of the first things we do is ensure that our reservoirs are as full as possible to meet demand. Having the reservoirs full allows us to shut down or decrease the flow of water into our treatment plant. This reduces the increased wear and tear on equipment, increased labor, and increased use of chemicals that it takes to treat the turbid water caused by the rain.

As explained above, we can rely on our stored water supplies for a little more than two days before having to fill them again. Of course, we will run through the treatment process during a storm if needed — we just try to avoid it. When source water levels and clarity are closer to normal, we go back to our regular pumping schedule.

This is where planning and the forecast really comes into play. If there is a weather event that will bring a short period of heavy rain with good weather for the next couple days afterward, we work to fill our reservoirs, and then shut down pumping and treatment at the beginning or middle of the event. We will then let the turbid water pass for a day or two before beginning pumping and treatment again.

If the event is going to last longer — whether it’s a full day or several days — we will continue pumping and treating on our normal schedule. We’ll shut down when it is over, or when it becomes apparent that the end of the storm is coming. Then we’ll let the worst of the turbid water pass, starting up the treatment plant when the turbidity is closer to normal.

If forecasters are calling for a major event — 3” or more of rain — we consider putting our secondary source online, just to be prepared. Our secondary source is usually the Lehigh River. Because of its size, it will typically take the river longer to become turbid than it does the smaller creeks. That means we can usually treat water from the Lehigh River longer during a storm, buying us more time. This method is most likely to be utilized during a hurricane.

Other Storm Steps

It’s not just water treatment that’s a priority during a storm, though. We also need to:

  • Drain down any wastewater basins. These are basins that hold water we’ve used to clean our systems, such as when we wash filters. By draining the basins ahead of time, we ensure we don’t overload the sewers later, when they’re at full capacity from storm water overflows.
  • Prepare for flooding along the river by removing any items within the plant property that could float away.
  • Check that our flood pump is working properly. It’s used to prevent our parking area near the Little Lehigh Creek from flooding out. 
  • Ensure we have enough treatment chemicals to make it through the storm — especially if we are going to need to treat the water for an extended period and use an exorbitant amount of materials, like the coagulant and chlorine.
  • Confirm which employees are on call in case we need extra help. This is a priority if something breaks during the storm.
  • Check and rearrange our filters to ensure they’re at optimal performance levels to handle increased turbidity.


As you can see, there’s a lot more to storm preparation at LCA than meets the eye. “Our team is hard at work each and every day, keeping aware of weather forecasts and determining potential actions needed to help us be prepared. We want to avoid any interruptions in quality or service to our customers,” says Liesel M. Gross, LCA’s CEO.

It’s all part of our commitment to bring you safe, reliable water.