Basement Water Damage Guides · Basement Water Damage Guides

Basement Sewage Backup: What to Do First

Basement sewage backup what to do first is a question with a clear answer: stay out, keep everyone away, and call a professional, because sewage is Category 3 black water and it is a professional-only job. A sewage backup brings waste water into a below-ground room, and that water carries contaminants that make it far more dangerous than rainwater or a burst pipe. No do-it-yourself sewage-cleanup advice is given here, because the cleaning involved is a matter for a professional.

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Basements are uncommon across most of California, and they exist mainly in older homes and some hillside areas, so this guidance applies to a smaller group of homes. For those homes, though, a sewage backup is the most serious form a basement flood can take. The [basement sewage cleanup](/basement-sewage-cleanup/) page describes the cleanup service in general terms.

What a sewage backup is in general terms

A sewage backup happens when waste water from drains or sewers flows back into a home instead of away from it, and a basement is often the room where it appears, because it sits at the lowest level. The backup can come from a blocked drain, a failed pump, or a sewer that has been overwhelmed by heavy rain, and the water it brings carries waste and contaminants. The signs are an odour, dark water, and waste in the water, and the room should be treated as dangerous.

No cause can be blamed for a backup in any specific home without a look in person, because the cause may be in the home's own drains or in the sewer beyond them. A professional looking at the home in person can say more about the cause than any general guide can.

Stay out and keep everyone away

Stay out of a basement that has taken sewage, and keep everyone away, including children and pets. Never enter a flooded basement, and never enter one that has taken sewage for any reason. Floodwater is not safe water, and sewage water is more dangerous still. Close the basement door if you can do so from dry ground, and tell everyone in the home that the room is out of bounds.

Do not try to save belongings from a basement that has taken sewage, and do not try to find the source of the backup yourself. The room will still be there when a professional arrives, and the belongings will still be there too. The only safe step is to stay out.

Basement Sewage Backup: What to Do First — California basement water damage guide

What not to do

Do not try to clean up sewage yourself, because no do-it-yourself sewage-cleanup advice is given here and the work is a professional-only job. Do not handle items that have been in contact with sewage, do not try to wash them yourself, and do not use a household vacuum, mop, or fan in a room that has taken sewage. Do not flush toilets or run water into drains that may be blocked, because that can make the backup worse.

Do not touch electrical items, switches, or outlets in standing water, and do not try to switch off the power from inside a flooded basement. If the power needs to be shut off, do it only from a dry place and only if it is safe to do so.

What to tell a professional

When you call a professional, say that the water is sewage, because that detail changes how the room must be dealt with. Describe what you can see from a safe distance: where the water is, how deep it looks, whether it is still rising, and whether it followed rain or appeared on a dry day. Say whether any drains in the home are backing up, and whether the odour is present in other rooms.

No availability or response-time claim is made here. The [basement sewage cleanup](/basement-sewage-cleanup/) page describes the cleanup service in general terms for California homeowners with basements.

Sewage in a home without a basement

Sewage can also affect a home without a basement, because waste water can back up into a ground-floor bathroom, a garage, or a crawl space. The safety rules are the same: stay out of the affected room, keep everyone away, and call a professional. No do-it-yourself sewage-cleanup advice is given here, whatever the room.

Basements are uncommon across most of California, so the equivalent problem for slab and crawl-space homes is often a ground-floor backup rather than a basement one. The service pages describe the scope in general terms, and the safety rules apply to every room that has taken sewage.

After the cleanup

After the cleanup, the room needs drying and restoration in general terms, and that work is described on the [basement water damage restoration](/basement-water-damage-restoration/) page. Do not re-enter the room until a professional has dealt with the water, and do not use the room or its drains until a professional has said it is safe. Keep a note of when the backup appeared and what was done, because that record helps both the cleanup company and any insurer you speak to.

The [basement sewage cleanup](/basement-sewage-cleanup/) page sets out the service in general terms for California homeowners.

Key Takeaways

A sewage backup happens when waste water from drains or sewers flows back into a home instead of away from it, and a basement is often the room where it appears, because it sits at the lowest level.
Stay out of a basement that has taken sewage, and keep everyone away, including children and pets.
Do not try to clean up sewage yourself, because no do-it-yourself sewage-cleanup advice is given here and the work is a professional-only job.
When you call a professional, say that the water is sewage, because that detail changes how the room must be dealt with.
Sewage can also affect a home without a basement, because waste water can back up into a ground-floor bathroom, a garage, or a crawl space.
After the cleanup, the room needs drying and restoration in general terms, and that work is described on the [basement water damage restoration](/basement-water-damage-restoration/) page.

Your Next Step

If this guide matches what you found at home, the next step is a visit — not a guess. Call and describe what you found, and the visit is arranged from what you describe. The Basement Sewage Cleanup page explains what that service covers, the Basement Flooding Cleanup page covers a related part of the job, and the services hub lists every service in one place.

While you wait, do not enter a flooded basement and do not touch switches, plugs or appliances in standing water. Floodwater is not safe water — keep pets and children clear of it.

Keep the guides on this site bookmarked: the first guide, the signs guide, and the preparation guide cover the checks worth repeating — after moving in, and after heavy rain.

Basement water damage help is available across California. See basement water damage cleanup in Glendora, CA for one local example, or find your town on the service areas page.