I recently moved into a home in Illinois that has a basement. I’m coming from Arizona and have never had a basement or actually knew about sump pumps until I started searching for a home.

Me and my wife were out of town a few weeks ago and there was some heavy rain and some snow melting as well and water must have backed up because there was water in my basement. No one could have been in my house to run any water or flush any toilets while we were out. I identified it coming from a floor drain in the laundry room and could see the water pattern go out. It did not seep in from the walls because they were dry and there was still dust on the walls. The plumber said my drain out pipe must be backed up and he rodded it from the outside.

My question is if the water came from the outside into the drain why didn’t it go into the basin of the sump pump and it should have pumped out to my backyard? The area around my sump pump was dry so I know water didn’t go into the basin and overflow.

If anyone could explain this to me because I feel like I’m missing something or not completely understand how this whole system is suppose to work.

  • The water didn't come from outside into your drain. There must've been a problem downstream somewhere in the municipal sewer system--a blockage or pressure from elsewhere. This isn't uncommon in flood situations, but it's probably not from your property.
    – isherwood
    Jan 31, 2020 at 17:56
  • Where is your sump pump and why is it there ? Meaning from where would the water be coming from so that a sump pump needs to evacuate it ? How would the water coming up from the drain get to the pump ? Presumably it would not have be installed to deal with main drain back ups ??
    – Alaska Man
    Jan 31, 2020 at 19:10
  • Isherwood, if that was the case wouldn't other neighbors have the same issue as me? Alaska Man, the sump pump is located on the other end of my basement from where the floor drain is located in the laundry room. For some reason I was under the impression that my home plumbing was connected to the sump pump but I believe the sump pump is just pulling water from the ground or near the foundation and pumping that water out.
    – Dan Khamis
    Feb 1, 2020 at 5:47

3 Answers 3


In some locations you cannot connect the sewer to the sump system, I understand this is not the discharge but sewage can be in that drain and pumping it outside could Create a health hazard. I have installed back flow preventers in the past to keep back pressure from entering, these do have there own problems but stop the city system from filling your basement with other peoples waste.

  • In my area it's not allowed to pump sumps into the sewer since it overloads the system (even though it's usually clean water).
    – isherwood
    Jan 31, 2020 at 18:22
  • I agree but that’s not what I was saying, I was saying the sump pit normally can not be connected to the drain because if the sewer backs up it would go into the pit then be pumped out on the ground as the op’s system does.
    – Ed Beal
    Jan 31, 2020 at 19:11

It seems that your floor drain and your sump pump are not connected which is often the case due to building codes.

The sump pit is designed so that any water that gets next to the foundation or under the floor (presumably concrete) will flow into the pit and collect until there is enough to trigger the pump switch which will then lift the water and expel it into a drain. These are needed because the basement is often BELOW the grade of the drain and will not drain using gravity alone.

Your floor drain, however, is a mystery here since we don't know where it goes.

In your case, however, is sounds like the floor drain is connected to a separate drain going who-knows-where and at the discharge point it's possible for water to backup and cause a backflow into your basement.

First, you want to identify WHERE the floor drain discharge is located and see if you can remedy the problem there. Perhaps it drains to a nearby ditch and that ditch has become clogged with debris. Perhaps it drains to the sewer and some obstruction has blocked the flow there. Failing that you might install a backflow valve to prevent any outside water from backup up into the basement.

As far as the sump, it sounds like there is not really an issue there although regular testing is always a good idea so that you are aware and can fix any problems before the need arises and another basement flooding situation occurs.

  • 1
    I completely disagree about floor drains leading to sump pits. That would be very illegal, as sewage (graywater) would potentially be ejected onto the street or lawn. I've actually never seen such a situation in many decades of basement exposure. Floor drains connect to municipal sewer or septic systems. Only drain tile (under the slab) or other types of foundation water management ducts lead to the sump pit.
    – isherwood
    Jan 31, 2020 at 17:58
  • @isherwood Where I live, floor drains are no longer allowed in the basement likely for the reason you give. If the water backs up through the drain, it could end up in the sump well.
    – JimmyJames
    Jan 31, 2020 at 18:05
  • What current code demands vs. what is out there already are often different. I've edited my answer to be more clear.
    – jwh20
    Jan 31, 2020 at 18:06
  • @JimmyJames, interesting. So furnace condensate lines, laundry overflows and the like don't exist or are pumped up?
    – isherwood
    Jan 31, 2020 at 18:21
  • 1
    @isherwood I had some elderly neighbors whose basement I was pumping out using my generator during an extended power outage. When I asked about why the floor drain was plugged, they said either the town incentivized it or required it when they put in a sump. I can't recall which. The cost of processing rain water as sewage is an issue in my area and so is sewage discharge during heavy storms.
    – JimmyJames
    Jan 31, 2020 at 18:29

As an addition to what Ed Beal stated, I'd surmise that your neighborhood has significant intermingling of storm water with the sanitary sewer. Hopefully not sewage into the storm sewer but the other way: storm water put into the sanitary sewer.

This is common in older neighborhoods. It was also allowable in a lot of neighborhoods to run everything to the sanitary up until sometime in the 20th century. In my current home, a previous owner had connected the sump pump outlet to the sanitary sewer. I know it's not the only home in the area that has/had a setup like that. It was somewhat understandable because the (literal) clay tile system was completely defunct.

When there's a heavy rain and/or melt, this results in the sanitary sewer backing up into homes. This is where Ed Beal's suggestion comes in.

If your home has some configuration like this, you should correct it and it should help somewhat. I had to have new drainage put in in order to run the sump properly. The sump pump connection actually caused issues when the sewer backed up because the sump water had no where to go but up the sanitary vent stack.

This kind of problem is also a major cause for sewage discharge into bodies of water that are sometimes used to supply drinking water. It's a big issue that we should all care about.

  • I should add that the backup was clean water and there was no foul odor from the water that was soaked in part of the carpet. d
    – Dan Khamis
    Feb 1, 2020 at 5:53
  • Another update to this was I called my home warranty to see if they can take a look. They came out and the guy was just looking for excuses to not do anything. The finally took a look at the discharge from the front of my house. He said since the water was not flowing that is more than likely that it is not linked to something inside my home.
    – Dan Khamis
    Feb 1, 2020 at 6:03
  • The had a heavy duty snake and rodded the discharge drain toward the street and there were some roots. Since the home warranty does not cover roots that is all he could do. During this process they probably did clear the line to a certain degree because the water was now flowing freely. Do you believe that the roots could cause a blockage and water to flow back into the floor drain? If the water was clean water would it be backed up from the sewer system?
    – Dan Khamis
    Feb 1, 2020 at 6:03
  • @DanKhamis re: clean water. If your neighborhood does have a significant amount of storm water going into the sanitary sewer, you won't tend notice much odor in heavy storm backups. It's the storm water that's overwhelming the system.
    – JimmyJames
    Feb 3, 2020 at 21:35
  • @DanKhamis re: roots. Absolutely roots can cause such issues. In older homes, the roots get in through the joints in the metal sewer drain and/or the clay drain tile. Now you have sieve that the water needs to go through which catches TP and other solids. You can put copper sulfate down the toilet to try to slow the roots but it's probably a safer move to have it 'roto-rooted' every few years.
    – JimmyJames
    Feb 3, 2020 at 21:39

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