It starts with sewage. A lot of it.
In the beginning, people got water from wells on their property and disposed of their own sewage, which may have been a pit in the back yard. Or not. In addition, transportation was by horse, which meant sewage literally ran in the streets. And into the drinking wells.
In 1871, the City built its first pumping station to pump water from the river. (Check out the picture to the right, including the guy standing in the trench being dug for the water main.)
Soon after, the City began to build sewers to remove sewage from the City. The sewers went to the river. The City was both drinking from the River and dumping its raw sewage into the River.
We were drinking our sewage.
From 1870 – 1910, annual typhoid epidemics occurred because residents are drinking contaminated water. 453 people died in 1883 from typhoid. 1897 there were over 3000 cases. Typhoid had a 10% mortality rate in Minneapolis. An 1882 study found dangerous amounts of animal and vegetable matter in the drinking water. In 1888, a pump station was added four miles north of the Falls, near Camden neighborhood in hopes of drinking less sewage. Over the next several decades, the water intakes are moved further north, ultimately to Columbia Heights and Fridley. 1909, Fecal matter is found in Minneapolis public water samples and is tied to the spread of typhoid.
In 1910, the City builds a water treatment plant in Columbia Heights. It begins to chlorinate its water. This is a huge and very expensive expansion of government as it requires not just the treatment plant but water towers, pressurized water mains throughout the City, pumping to higher parts of the City and other expensive infrastructure.
Typhoid deaths plunge.
But we are still dumping our sewage into the River. By the early 1920s, three million cubic yards of sewage and scum fouled the Mississippi. The Mississippi was described in the 1930’s as “having floating islands of sewage solids, scum on the water surface, and an abundance of dead fish.” City smelled bad. Minneapolis flour mills began dumping flour dust into the river, creating “dough balls” that added to the stench and pollution. “
St Paul gets much of its drinking water from the Mississippi River. As Minneapolis dumps its sewage into the river, this means St Paul is drinking Minneapolis sewage. In 1933, the Minnesota State Board of Health ordered the creation of the Minneapolis-St. Paul Sanitary District. The Pigs Eye Treatment Plant opens in 1938. It is the first wastewater treatment plant for a major city on Mississippi and is hailed as an engineering wonder and savior of the River. Within four months, the floating mats of stinking sludge and scum were gone. Within two years, fish returned to Twin Cities waters. But the treatment plant is hugely expensive and also requires a network of deep sewer tunnels, pumps and other expensive infrastructure.
When the region starts to grow, sewer treatment plants are built around the region. At one point, there are 33 sewer treatment plants throughout the Twin Cities. Many of them are not working well and raw sewage is being discharged on an average of at least once per day.
Also, water treatment itself changed. In 1938, treatment was very basic. By 1966, they added microscopic organisms to feed on organic wastes. In 1982, they reduced heavy metals. In 1984, effluent nitrification was added, breaking down ammonia. In 1986, they added chlorine removal. In 1998 they added removal of mercury. In 2008, they added removal of phosphorus. Most of the plants in the region are not able to meet these higher standards.
With the Clean Water Act in 1972, cities now have to deal with these sewage problems. Dumping raw sewage is not OK. There were 33 sewage treatment plants but most are not meeting basic requirements of treatment. So, the region begins to plan for new sewer treatment plants throughout the region. But how big? You don’t want to under-size them because they are very expensive to add to. Conversely, because they are so expensive, you don’t want to overbuild. Because of this, you need a plan for where people are going to live and where they are going to flush. Today, we have eight sewer treatment plants in the region.
Because of this, the Met Council does forecasting of population growth. This lets them know where to plan for sewage infrastructure. They also plan for other infrastructure like transportation, water, regional parks, affordable housing and other regional needs. If you want to see these population estimates, they are available here:
https://metrocouncil.org/Data-and-Maps/Data/Census,-Forecasts,-Estimates-NEW/Council-Forecasts.aspx
A big part of this forecasting is not about existing development but about where the sewers will extend or expand. Without sewers, people deal with their sewage through septic systems. Septic systems require septic fields for the sewage to sink into the surrounding ground, which means low density development. For density to reach the levels of a city, you need sewers. The Met Council plans for where the sewer system will extend by controlling what is called the Municipal Urban Service Area or MUSA line. This picture is the MUSA line. The purple is where they plan to expand the MUSA line in the next 20 years.
This is important because it shows where large amounts of new housing will go in. Because of this, the MUSA is very important. 
The Metropolitan Council tells cities how much growth to plan for so the Met Council know how much sewer capacity to plan for. But there are also other regional systems that need planning.
Please read Part 2.