[00:01] Wichita Falls, Texas, went through the worst&nbsp; drought in its history in 2011 and 2012. For&nbsp;&nbsp; two years in a row, the area saw its average&nbsp; annual rainfall roughly cut in half, decimating&nbsp;&nbsp;
[00:13] the levels in the three reservoirs used for the&nbsp; city’s water supply. Looking ahead, the city&nbsp;&nbsp; realized that if the hot, dry weather continued,&nbsp; they would be completely out of water by 2015.&nbsp;&nbsp;
[00:25] Three years sounds like a long runway, but when&nbsp; it comes to major public infrastructure projects,&nbsp;&nbsp; it might as well be overnight. Between&nbsp; permitting, funding, design, and construction,&nbsp;&nbsp; three years barely gets you to the starting&nbsp; line. So the city started looking for other&nbsp;&nbsp;
[00:40] options. And they realized there was one source of&nbsp; water nearby that was just being wasted - millions&nbsp;&nbsp; of gallons per day just being flushed down&nbsp;the Wichita River. I’m sure&nbsp;&nbsp;
[00:52] you can guess where I’m going with this. It was&nbsp; the effluent from their sewage treatment plant. The city asked the state regulators if they could&nbsp; try something that had never been done before at&nbsp;&nbsp; such a scale: take the discharge pipe from the&nbsp; wastewater treatment plant and run it directly&nbsp;&nbsp;
[01:07] into the purification plant that produces most of&nbsp; the city’s drinking water. And the state said no.&nbsp;&nbsp; So they did some more research and testing&nbsp; and asked again. By then, the situation had&nbsp;&nbsp; become an emergency. This time, the state said&nbsp; yes. And what happened next would completely&nbsp;&nbsp;
[01:24] change the way cities think about water.&nbsp; I’m Grady and this is Practical Engineering.
[01:38] You know what they say, wastewater happens.&nbsp; It wasn’t that long ago that raw sewage was&nbsp;&nbsp; simply routed into rivers, streams, or&nbsp; the ocean to be carried away. Thankfully,&nbsp;&nbsp; environmental regulations put a stop to&nbsp; that, or at least significantly curbed&nbsp;&nbsp;
[01:53] the amount of wastewater being set loose without&nbsp; treatment. Wastewater plants across the world do&nbsp;&nbsp; a pretty good job of removing pollutants these&nbsp; days. In fact, I have a series of videos that&nbsp;&nbsp; go through some of the major processes&nbsp; if you want to dive deeper after this.&nbsp;&nbsp;
[02:08] In most places, the permits that allow these&nbsp; plants to discharge set strict limits on&nbsp;&nbsp; contaminants like organics, suspended solids,&nbsp; nutrients, and bacteria. And in most cases,&nbsp;&nbsp; they’re individualized. The permit limits&nbsp; are based on where the effluent will go,&nbsp;&nbsp;
[02:24] how that water body is used, and how well it can&nbsp; tolerate added nutrients or pollutants. And here’s&nbsp;&nbsp; where you start to see the issue with reusing&nbsp; that water: “clean enough” is a sliding scale.
[02:36] Depending on how water is going to be used&nbsp; or what or who it’s going to interact with,&nbsp;&nbsp; our standards for cleanliness vary. If&nbsp; you have a dog, you probably know this.&nbsp;&nbsp; They should drink clean water, but a few&nbsp; sips of a mud puddle in a dirty street,&nbsp;&nbsp;
[02:52] and they’re usually just fine. For you,&nbsp; that might be a trip to the hospital.&nbsp;&nbsp; Natural systems can tolerate a pretty wide range&nbsp; of water quality, but when it comes to drinking&nbsp;&nbsp; water for humans, it should be VERY clean. So&nbsp; the easiest way to recycle treated wastewater&nbsp;&nbsp;
[03:08] is to use it in ways that don’t involve&nbsp; people. That idea’s been around for a while. A lot of wastewater treatment plants apply&nbsp; effluent to land as a disposal method,&nbsp;&nbsp; avoiding the need for discharge to a natural&nbsp; water body. Water soaks into the ground,&nbsp;&nbsp;
[03:24] kind of like a giant septic system. But that&nbsp; comes with some challenges. It only works if&nbsp;&nbsp; you’ve got a lot of land with no public&nbsp; access, and a way to keep the spray from&nbsp;&nbsp; drifting into neighboring properties. Easy&nbsp; at a small scale, but for larger plants,&nbsp;&nbsp;
[03:38] it just isn’t practical engineering. Plus,&nbsp; the only benefits a utility gets from the&nbsp;&nbsp; effluent are some groundwater recharge and&nbsp; maybe a few hay harvests per season. So,&nbsp;&nbsp; why not send the effluent to someone else&nbsp; who can actually put it to beneficial use?
[03:53] If only it were that simple. As soon as a utility&nbsp; starts supplying water to someone else, things get&nbsp;&nbsp; complicated because you lose a lot of control over&nbsp; how the effluent is used. Once it's out of your&nbsp;&nbsp;
[04:05] hands, so to speak, it’s a lot harder to make&nbsp; sure it doesn’t end up somewhere it shouldn’t,&nbsp;&nbsp; like someone’s mouth. So, naturally, the&nbsp; permitting requirements become stricter.&nbsp;&nbsp; Treatment processes get more complicated&nbsp; and expensive. You need regular monitoring,&nbsp;&nbsp;
[04:20] sampling, and laboratory testing. In many&nbsp; places in the world, reclaimed water runs&nbsp;&nbsp; in purple pipes so that someone doesn’t&nbsp; inadvertently connect to the lines thinking&nbsp;&nbsp; they’re potable water. In many cases, you&nbsp; need an agreement in place with the end user,&nbsp;&nbsp;
[04:34] making sure they’re putting up signs, fences,&nbsp; and other means of keeping people from drinking&nbsp;&nbsp; the water. And then you need to plan for&nbsp; emergencies - what to do if a pipe breaks,&nbsp;&nbsp; if the effluent quality falls below the standards,&nbsp; or if a cross-connection is made accidentally.
[04:50] It’s a lot of work - time, effort, and cost&nbsp; - to do it safely and follow the rules. And&nbsp;&nbsp; those costs have to be weighed against&nbsp; the savings that reusing water creates.&nbsp;&nbsp; In places that get a lot of rain or snow, it’s&nbsp; usually not worth it. But in many US states,&nbsp;&nbsp;
[05:06] particularly those in the southwest, this is a&nbsp; major strategy to reduce the demand on fresh water&nbsp;&nbsp; supplies. Think about all the things we use water&nbsp; for where its cleanliness isn’t that important.&nbsp;&nbsp;
[05:18] Irrigation is a big one - crops, pastures,&nbsp; parks, highway landscaping, cemeteries - but&nbsp;&nbsp; that’s not all. Power plants use huge amounts&nbsp; of water for cooling. Street sweeping, dust&nbsp;&nbsp; control. In nearly the entire developed world,&nbsp; we use drinking-quality water to flush toilets!
[05:35] You can see where there might be cases where&nbsp; it makes good sense to reclaim wastewater,&nbsp;&nbsp; and despite all the extra challenges, its use&nbsp; is fairly widespread. One of the first plants&nbsp;&nbsp; was built in 1926 at Grand Canyon Village which&nbsp; supplied reclaimed water to a power plant and for&nbsp;&nbsp;
[05:52] use in steam locomotives. Today, these systems can&nbsp; be massive, with miles and miles of purple pipes&nbsp;&nbsp; run entirely separate from the freshwater piping.&nbsp; I’ve talked about this a bit on the channel&nbsp;&nbsp; before. I used to live near a pair of water&nbsp; towers in San Antonio that were at two different&nbsp;&nbsp;
[06:07] heights above ground. That just didn’t make any&nbsp; sense until I realized they weren’t connected;&nbsp;&nbsp; one of them was for the reclaimed water system&nbsp; that didn’t need as much pressure in the lines.&nbsp;&nbsp; Places like Phoenix, Austin, San Antonio, Orange&nbsp; County, Irvine, and Tampa all have major water&nbsp;&nbsp;
[06:24] reclamation programs. And it’s not just a&nbsp; US thing. Abu Dhabi, Beijing, and Tel Aviv&nbsp;&nbsp; all have infrastructure to make beneficial use of&nbsp; treated municipal wastewater, just to name a few.
[06:36] Because of the extra treatment and&nbsp; requirements, many places put reclaimed&nbsp;&nbsp; water in categories based on how it gets&nbsp; used. The higher the risk of human contact,&nbsp;&nbsp; the tighter the pollutant limits get. For example,&nbsp; if a utility is just selling effluent to farmers,&nbsp;&nbsp;
[06:52] ranchers, or for use in construction, exposure&nbsp; to the public is minimal. Disinfecting the&nbsp;&nbsp; effluent with UV or chlorine may be enough to&nbsp; meet requirements. And often that’s something&nbsp;&nbsp; that can be added pretty simply to an existing&nbsp; plant. But many reclaimed water users are things&nbsp;&nbsp;
[07:07] like golf courses, schoolyards, sports&nbsp; fields, and industrial cooling towers,&nbsp;&nbsp; where people are more likely to be exposed.&nbsp; In those cases, you often need a sewage plant&nbsp;&nbsp; specifically designed for the purpose or&nbsp; at least major upgrades to include what the&nbsp;&nbsp;
[07:22] pros call tertiary treatment processes - ways to&nbsp; target pollutants we usually don’t worry about and&nbsp;&nbsp; improve the removal rates of the ones we do. These&nbsp; can include filters to remove suspended solids,&nbsp;&nbsp;
[07:34] chemicals that bind to nutrients, and stronger&nbsp; disinfection to more effectively kill pathogens. This creates a conundrum, though. In many cases,&nbsp; we treat wastewater effluent to higher standards&nbsp;&nbsp;
[07:46] than we normally would in order to reclaim&nbsp; it, but only for nonpotable uses, with strict&nbsp;&nbsp; regulations about human contact. But if it’s not&nbsp; being reclaimed, the quality standards are lower,&nbsp;&nbsp;
[07:58] and we send it downstream. If you know how rivers&nbsp; work, you probably see the inconsistency here.&nbsp;&nbsp; Because in many places, down the river, is&nbsp; the next city with its water purification&nbsp;&nbsp; plant whose intakes, in effect, reclaim that&nbsp; treated sewage from the people upstream.
[08:15] This isn’t theoretical - it’s just the reality&nbsp; of how humans interact with the water cycle.&nbsp;&nbsp; We’ve struggled with the problems it causes for&nbsp; ages. In 1906, Missouri sued Illinois in the&nbsp;&nbsp; Supreme Court when Chicago reversed their&nbsp; river, redirecting its water (and all the&nbsp;&nbsp;
[08:31] city’s sewage) toward the Mississippi River. If&nbsp; you live in Houston, I hate to break it to you,&nbsp;&nbsp; but a big portion of your drinking water comes&nbsp; from the flushes and showers in Dallas. There&nbsp;&nbsp; have been times when wastewater effluent makes&nbsp; up half of the flow in the Trinity River.
[08:46] But the question is: if they can do it, why&nbsp; can’t we? If our wastewater effluent is already&nbsp;&nbsp; being reused by the city downstream to purify&nbsp; into drinking water, why can’t we just keep&nbsp;&nbsp; the effluent for ourselves and do the same&nbsp; thing? And the answer again is complicated.
[09:03] It starts with what’s called an environmental&nbsp; buffer. Natural systems offer time to detect&nbsp;&nbsp; failures, dilute contaminants, and even&nbsp; clean the water a bit—sunlight disinfects,&nbsp;&nbsp;
[09:15] bacteria consume organic matter. That’s the big&nbsp; difference in one city, in effect, reclaiming&nbsp;&nbsp; water from another upstream. There’s nature in&nbsp; between. So a lot of water reclamation systems,&nbsp;&nbsp;
[09:27] called indirect potable reuse, do the same thing:&nbsp; you discharge the effluent into a river, lake,&nbsp;&nbsp; or aquifer, then pull it out again later for&nbsp; purification into drinking water. By then,&nbsp;&nbsp;
[09:39] it’s been diluted and treated&nbsp; somewhat by the natural systems. Direct potable reuse projects skip the buffer&nbsp; and pipe straight from one treatment plant&nbsp;&nbsp; to the next. There’s no margin for error&nbsp; provided by the environmental buffer. So,&nbsp;&nbsp;
[09:54] you have to engineer those same protections&nbsp; into the system: real-time monitoring,&nbsp;&nbsp; alarms, automatic shutdowns, and&nbsp; redundant treatment processes. Then there’s the issue of contaminants of emerging&nbsp; concern: pharmaceuticals, PFAS [P-FAS], personal&nbsp;&nbsp;
[10:09] care products - things that pass through people&nbsp; or households and end up in wastewater in tiny&nbsp;&nbsp; amounts. Individually, they’re in parts per&nbsp; billion or trillion. But when you close the&nbsp;&nbsp; loop and reuse water over and over, those&nbsp; trace compounds can accumulate. Many of these&nbsp;&nbsp;
[10:26] aren’t regulated because they’ve never reached&nbsp; concentrations high enough to cause concern,&nbsp;&nbsp; or there just isn’t enough knowledge about&nbsp; their effects yet. That’s slowly changing, and&nbsp;&nbsp; it presents a big challenge for reuse projects.&nbsp; They can be dealt with at the source by regulating&nbsp;&nbsp;
[10:42] consumer products, encouraging proper disposal&nbsp; of pharmaceuticals (instead of flushing them),&nbsp;&nbsp; and imposing pretreatment requirements&nbsp; for industries. It can also happen at the&nbsp;&nbsp; treatment plant with advanced technologies&nbsp; like reverse osmosis, activated carbon,&nbsp;&nbsp;
[10:57] advanced oxidation, and bio-reactors that&nbsp; break down micro-contaminants. Either way,&nbsp;&nbsp; it adds cost and complexity to&nbsp; a reuse program. But really,&nbsp;&nbsp; the biggest problem with wastewater reuse&nbsp; isn’t technical - it’s psychological.
[11:12] The so-called “yuck factor” is real. People don’t&nbsp; want to drink sewage. Indirect reuse projects&nbsp;&nbsp; have a big benefit here. With some nature in&nbsp; between, it’s not just treated wastewater;&nbsp;&nbsp;
[11:24] it’s a natural source of water with&nbsp; treated wastewater in it. It’s kind&nbsp;&nbsp; of a story we tell ourselves, but we lose&nbsp; the benefit of that with direct reuse:&nbsp;&nbsp; Knowing your water came from a toilet—even&nbsp; if it’s been purified beyond drinking water&nbsp;&nbsp;
[11:40] standards—makes people uneasy. You might&nbsp; not think about it, but turning the tap on,&nbsp;&nbsp; putting that water in a glass, and taking a drink&nbsp; is an enormous act of trust. Most of us don’t&nbsp;&nbsp; understand water treatment and how it happens&nbsp; at a city scale. So that trust that it’s safe&nbsp;&nbsp;
[11:56] to drink largely comes from seeing other people do&nbsp; it and past experience of doing it over and over&nbsp;&nbsp; and not getting sick. The issue is that, when&nbsp; you add one bit of knowledge to that relative&nbsp;&nbsp;
[12:08] void of understanding - this water came directly&nbsp; from sewage - it throws that trust off balance.&nbsp;&nbsp; It forces you not to rely not on past experience&nbsp; but on the people and processes in place,&nbsp;&nbsp;
[12:20] most of which you don’t understand deeply, and&nbsp; generally none of which you can actually see.&nbsp;&nbsp; It’s not as simple as just revulsion.&nbsp; It shakes up your entire belief system. And there’s no engineering fix for that.&nbsp; Especially for direct potable reuse,&nbsp;&nbsp;
[12:35] public trust is critical. So on top of&nbsp; the infrastructure, these programs also&nbsp;&nbsp; involve major public awareness campaigns.&nbsp; Utilities have to put themselves out there,&nbsp;&nbsp; gather feedback, respond to questions,&nbsp; be empathetic to a community’s values,&nbsp;&nbsp;
[12:50] and try to help people understand how we ensure&nbsp; water quality, no matter what the source is. But also, like I said, a lot of that trust&nbsp; comes from past experience. Not everyone can&nbsp;&nbsp; be an environmental engineer or licensed treatment&nbsp; plant operator. And let’s be honest - utilities&nbsp;&nbsp;
[13:07] can’t reach everyone. How many public meetings&nbsp; about water treatment have you ever attended? So,&nbsp;&nbsp; in many places, that trust is just going&nbsp; to have to be built by doing it right,&nbsp;&nbsp; doing it well, and doing it for a long&nbsp; time. But, someone has to be first.
[13:25] In the U.S., at least on the city scale, that&nbsp; drinking water guinea pig was Wichita Falls.&nbsp;&nbsp; They launched a massive outreach campaign, invited&nbsp; experts for tours, and worked to build public&nbsp;&nbsp;
[13:38] support. But at the end of the day, they didn’t&nbsp; really have a choice. The drought really was that&nbsp;&nbsp; severe. They spent nearly four years under intense&nbsp; water restrictions. Usage dropped to a third of&nbsp;&nbsp;
[13:50] normal demand, but it still wasn’t enough. So, in collaboration with state regulators,&nbsp;&nbsp; they designed an emergency direct potable reuse&nbsp; system. They literally helped write the rules as&nbsp;&nbsp;
[14:02] they went, since no one had ever done it before.&nbsp; After two months of testing and verification,&nbsp;&nbsp; they turned on the system in July&nbsp; 2014. It made national headlines. The project ran for exactly one year. Then, in&nbsp; 2015, a massive flood ended the drought and filled&nbsp;&nbsp;
[14:19] the reservoirs in just three weeks. The emergency&nbsp; system was always meant to be temporary. Water&nbsp;&nbsp; essentially went through three treatment plants:&nbsp; the wastewater plant, a reverse osmosis plant,&nbsp;&nbsp; and then the regular water purification&nbsp; plant. That’s a lot of treatment,&nbsp;&nbsp;
[14:35] which is a lot of expense, but they needed to have&nbsp; the failsafe and redundancy to get the state on&nbsp;&nbsp; board with the project. The pipe connecting&nbsp; the two plants was above ground and later&nbsp;&nbsp; repurposed for the city’s indirect potable&nbsp; reuse system, which is still in use today.
[14:51] In the end, they reclaimed nearly two billion&nbsp; gallons of wastewater as drinking water. And&nbsp;&nbsp; they did it with 100% compliance with&nbsp; the standards. But more importantly,&nbsp;&nbsp; they showed that it could be done,&nbsp; essentially unlocking a new branch&nbsp;&nbsp;
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