How do we get clean water out of the tap?
It’s a feat of chemistry, physics and engineering and needs constant maintenance
From left, a lead pipe, a corroded steel pipe, and a lead pipe treated with protective orthophosphate. Lead pipes cause health problems and drive up water bills. Photo courtesy Environmenal Protection Agency.
Editor’s note: Ann Johnson Stewart, a civil engineer and former state senator, is writing an occasional series of columns for the Reformer on infrastructure issues.
I recently returned from a trip to Costa Rica. Our hosts advised us that the tap water was “probably safe” to drink. I chose not to. Unfortunately, that’s a familiar experience for many U.S. citizens here at home; even for some who live in Minnesota.
In general, Minnesota’s drinking water is safe, but it’s hard to ignore the constant news about both the quantity and the quality of drinking water across the U.S.
Safety issues in Jackson, Miss., Flint, Mich., and Philadelphia illustrate how real the problem is.
And it’s not just quality, it’s quantity. The water supply impacts business and economic growth, with water needed for manufacturing in direct competition with that for drinking: choosing one over the other is not easy. We want microchip and semiconductors to be produced locally, but the process requires enormous amounts of water.
The Colorado River provides water to about 40 million people, and it is slowly drying up. Arizona has done the unthinkable for a Sun Belt region: Curtailed growth around Phoenix because of water shortages. There’s more: States along the Colorado River just agreed to leave a major portion of their water supply in the river in hopes of keeping Lake Powell and Lake Mead from falling so low that they can no longer produce hydropower. That water is badly needed for energy production, but the deal cost more than $1 billion to pay farmers and others to forgo water use, meaning unsown fields and potential job losses in some of our country’s major agricultural regions.
Remember the (unsuccessful) proposal to pipe drinking water from Dakota County to western states? Get ready for that to become a common request — or even demand — as safe and plentiful drinking water becomes more valuable.
Water may be all around us here, but it’s still precious. Most of our drinking water comes from underground aquifers (or layers of rock that hold water), with some coming from rivers and lakes. In the metro area, our water is locally sourced by each city (with some cities sharing water sources; local water disputes have also been in the news!)
The widespread availability of drinkable water is one of the great technological advances of modern life, but it’s complicated and requires significant resources. Here’s a brief overview of how water gets from the ground to our tap:
Typically, water treatment is achieved using simple chemistry. If you’ve taken a chemistry class, you probably remember the periodic table. Each element on it has a positive or negative charge. So, if we need to remove a certain element (like iron), we add a chemical that reacts with it (like oxygen or calcium). That element binds to the dirt and dissolved particles in the water, forming larger particles called “floc.” Usually, that’s all the treatment that’s needed: The floc is heavier than the water, so it drops to the bottom of the tank. We design the tanks so that clean water flows out the top and the floc settles on the bottom (where it can be removed).
After clear water flows out, it’s forced through filters made of sand and charcoal. This causes more flocculation, removing more dissolved particles such as dust, parasites, bacteria and viruses.
If you visit a water treatment plant (I suggest the one just north of Duluth, which is open for tours) you’ll learn how these filters work, and how the filters are cleaned by running clean water backwards through them to force out the collected materials. The water is then disinfected with chlorine to kill any remaining parasites, bacteria, viruses and germs. Some cities add fluoride to prevent tooth decay.
One more thing from chemistry class: remember pH? It’s a measure of how basic or acidic something is. Chemicals (like salt) can be added to adjust the pH of the water to “harden” or “soften” it (much like you do in your home). The pH also impacts the corrosiveness of water, which can impact the condition of the pipes.
Many old water pipes are made of lead, and without taking preventive measures, the lead from the pipes may leach into the water supply. Lead is a dangerous neurotoxin, especially for children. While the most effective solution is to replace lead pipes entirely (and thanks to the Infrastructure Investment and Jobs Act, we now have money to do that), water utilities usually add some form of phosphate to the water supply to create a protective film between the lead pipe and the water flowing through it.
This works fine except when it doesn’t: The water problems in Flint serve as a tragic example. The city changed its water source to one that contained significantly more chloride than they’d been using. They did not add the required phosphate to provide the protective film between the water and the pipes, which caused corrosion, putting high lead levels in the water.
As noted, the chemistry in water treatment is both simple and important.
And while we’re talking about lead pipes: Replacing them is not so easy. For example, the city of St. Paul (like many others) is in the process of replacing miles of lead water mains, which are the pipes that feed the entire system. This is great and will do much to improve the safety of our drinking water supply. However, cities are typically only responsible for maintaining the piping to a home’s service valve (often called the “curb stop” because it’s located behind the curb). The service line is the pipe between the curb stop and the meter, and many older homes (built before 1986) contain both lead service lines and plumbing, which are the homeowner’s responsibility to replace. That requires ripping out walls and replacing service pipes; both are very expensive and disruptive operations.
St. Paul is using federal funds from the Infrastructure Investment and Jobs Act to help 26,000 homeowners replace the pipe from the meter to their homes, but the internal plumbing and soldering is still lead in many houses. Other cities have similar programs, and the Legislature smartly allocated more money into the effort this year.
Bonding is the only way many small towns can fund improvements or maintenance of their drinking water systems. In Minnetonka, our water bill is about $40 per month. That’s not the case everywhere: A small town still needs a distribution system, and with the loss of population comes the loss of residents paying for that system.
For a small town —like, say, Red Lake Falls — to fund the replacement of its aging water tower, each resident would be assessed thousands of dollars. Residents in Red Lake Falls pay five times as much for their drinking water as I do (and no, that is not a typo).
Also: Small towns do not have the property tax base to finance projects on their own. Just this session, more than 60 Minnesota communities submitted funding requests to the Senate Capital Investment Committee totaling more than $500 million just for drinking water treatment projects. The list is long and represents every corner of Minnesota (but mostly rural areas).
Safe drinking water is important and should be expected in Minnesota. We must maintain our systems. One broken water main in Jackson, Mississippi, is spewing 5 million gallons each day. So, in Jackson (where residents spent months drinking bottled water due to poor water quality), water for 50,000 people every day is literally running down the drain because of a broken water main.
Even worse: The break has gone unrepaired since 2016, and until the Biden administration came to the rescue, the city had no resources to fix it.
Let’s not let that happen here.
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