Yup…Chicago (where I live) did this and big storms would mean sewage would overflow into the lake. While not an ecological disaster it’s not great and if you live down-current it’s pretty awful (hi Indiana).
Say hello to Chicago’s Tunnel and Reservoir Plan (TARP), also sometimes called the Deep Tunnel. It’s very ambitious and (I think) getting near completion after some huge amount of work (I want to say it started in the 1970s…whatever the case this has been a looooong project). And it still might not be enough in all cases but it has improved things.
Municipal water towers maintain pressure and reduce wear on pumps by virtue of being reservoirs to store excess water at night that drains down during the day. I don’t see why building water towers are any different. The India example may need a bigger tank than a NYC building of the same size, especially if they only get two out of 24 hours of the day of service, but the principle is the same.
The higher the water tower the higher the water pressure at the bottom of the outflow pipe at street level. You are back to finding ways to deal with that (and engineers have but it’s more than build a water tower and attach a pipe).
ETA: Let’s take the most extreme. Say you put a water tower on the top of the Burj Khalifa (tallest building in the world currently). Water pressure at street level would be close to 1,200 PSI (not quite but near enough).
I guess that technically a water tower is a reservoir, but it’s a lot lower volume than the ones that we call reservoirs.
And I’m still not sure why anyone ever had the idea to make combined-sewer systems. It just seems like all downside to me… Why not completely enclose the sewage, so the stormwater never gets into it at all?
I do not know. My guess would be it is how a city evolves. They started small and if you are a few dozen people making a drainage system for rain and sewage you do it the simple and fast way. Why not? Then the city grows and they just keep going with that. Then one day there is a realization this wasn’t the best way to do things.
ETA: Also, those early settlers are likely clueless when it comes to engineering a well designed sewage and drainage system. They did what made sense and that was a combined system. We know better now but they didn’t.
Here in very flat Florida I ran an 8-story condo complex. 8 stories is by no means a tall building. Our water system had two large booster pumps operating in parallel which took city water coming up out of the city’s underground piping and pumped them up to a distribution manifold on the roof = what would be the 9th floor if it was enclosed. From there it distributed across the roof to the top of each service stack. And then straight back down to the ground with branches off at each floor to service each unit. With a pressure regulator at each service entrance to each branch.
We did not have a header tank of any size on the roof. When the power failed, if the one pump on the emergency generator didn’t get power, then the water pressure and water volume declined to “not very damned much”. It wasn’t a total water outage; you could draw water at a barely adequate pace to cook & wash hands. But baths and showers weren’t going to happen.
We had a separate pump and fire manifold to provide water to the fire suppression stuff around the building.
Standard installation in anything much taller than 4 stories.
I traveled quite a bit in India, it is a very big country, so I went to the provinces of Gujurat and Rajasthan, with a side trip to Agra in Utter Pradesh for the Taj Mahal - visiting both tiny villages and big cities.
The big cities had great water supply and sanitation, the villages less so.
In one tiny, beautiful village, Bundi (made famous by Rudyard Kipling as the place he wrote “The Jungle Book”) the water supply in certain areas, is open ditches running down the side of narrow streets, with cattle and humans all sharing and polluting the same supply. I saw both cow and human turds in those ditches.
So, basically a judgement call every time I was thirsty. The same in Indonesia, except, there is widespread “water fraud”, where emply “mineral” bottles would be refilled from the fairly unsafe mains, then sold on.
I managed to avoid any negative consequences by being very careful, and both climates require a lot of rehydration.
Here’s why: the combined sewer systems were all built before the sanitary sewage flow was treated via wastewater treatment plants. Instead the sanitary flow was diverted into the nearest water body. Since the stormwater flow was going to the same place, it was cheaper and easier to only build one larger pipe that could handle both flows. And they figured that every time it rained, it would flush the sewers out.
Here in the U.S., these types of systems were typically built in the closing decades of the 19th century. They were a big improvement over inadequate septic systems or letting sewage flow down the gutters in the streets, plus they also conveyed stormwater flow to alleviate street flooding in storms. Of course the downside of these systems is that they pollute the environment with untreated sewage.
When they eventually realized that the sewage should be treated (around the 1920s or so), they built wastewater treatment plants sufficiently large to treat the sanitary flow only (the so-called dry weather flow). But when it rains a lot, it overwhelms the plant and they have to bypass the plant (so-called Combined System Overlows, or CSOs). The thought was that they had no choice, that the sanitary flow got treated in dry weather, and during wet weather at least the flow would be diluted with stormwater.
These CSOs are all now banned here in the U.S., and utilities and municipalities are under pressure to eliminate them by regulatory authorities. The way to fix them is to build a whole separate system of pipes all over the city (i.e. sewer separation projects), or figure out a way to store all of that combined flow during a storm until it can all be treated. My utility has spent billions of dollars to address our CSOs using both approaches. Other older cities with combined systems are doing the same thing.
India has been notoriously backwards compared to the rest of the world. Considering standing on the bank of the Ganges and taking a shit in public is still part of their culture, they have come a relatively long way.
Unfortunate that a tremendous amount of urban growth in the USA occurred in that ~50 year interval from 1870 to 1920.
A further shame that it took another WAG 50 years (to 1970) to begin to grapple with the reality that combined systems are an ongoing disaster that must be remediated, not merely put up with.
Dumping untreated sewage into the river is FUBAR, but water emergencies happen all the time, not just in India. Corpus Christi, Tehran, Johannesburg, Perth, Istanbul, you name it.
I remember a few decades ago, an investigative reporter team from the CBC did a test in Halifax. They dumped a dye into a public toilet near the harbor, then went to the nearby sewer outlet to see a brightly coloured overflow appearing in the water where the pipe came out. Typical of most cities, it had a long way to go the install separate sewage and storm drains, and install a sewage treatment plant. The logic that “the tide sweeps it out to sea” fails as the population increases significantly.
Indeed, and even then it took another few decades to force public utilities and municipalities to fully address the problem. The issue is that the fix was so expensive that it took state and federal legal action to force the issue, which led to fines, consent orders, and consent decrees in order to get municipalities to take effective corrective measures with actionable deadlines.
BTW, upon re-reading my post, I will nitpick myself: CSOs actually stand for “Combined Sewer Overflows.” I use the acronym so much I forgot what it is actually short for.