Why storms here behave differently
The Hill Country sits on limestone with comparatively thin soil over it. Water that would soak into deeper ground elsewhere has nowhere to go here, so it moves across the surface instead — fast, and in volume.
That is the same geology behind the region's flash flood reputation, and it is why a storm that would be unremarkable elsewhere produces a lot of moving water here.
For plumbing, the consequences are indirect but consistent. Systems designed for a certain flow get more than that. Ground that was dry and shrunken takes on water rapidly and swells. And anywhere water can pond against a structure, it does.
None of that damages plumbing on its own. It is the combination with what is already marginal — a partly blocked line, a sagging lateral, a foundation with poor grading — that produces the call.
Sewer backups, and the valve that prevents them
The consequence people least expect. During heavy rain a municipal main can surcharge — take on more water than it can carry, through infiltration and inflow into the system.
When that happens, the sewage in the main has to go somewhere, and it looks for the lowest available opening. If that is the lowest fixture in the lowest house on the run, it comes up there.
This is not your line failing, and nothing you do inside the house prevents it. Habits, drain cleaning and careful use are all irrelevant to a backup arriving from the street.
A backwater valve is the answer — a one-way flap in the lateral that passes normal outflow and closes against reverse flow. Worth considering if your house sits low relative to the street, if you have had a backup that coincided with heavy rain, or if you have finished space at the lowest level.
If yours already has one, it needs to be accessible and inspected. A valve silted up or jammed open protects nothing.
Worth knowing
The tell that distinguishes a street-side backup from your own blockage: timing. A backup that happens during or just after heavy rain, in a house whose drains were fine the day before, is usually the main surcharging rather than your lateral blocking.
What the ground does
Expansive clay swells as it takes on water. After a long dry spell — which is how our summers end — the ground has shrunk, and heavy rain reverses that quickly.
That movement is transmitted to anything buried. Over repeated cycles it pulls sewer joints apart, drops sags into lines that were laid to fall correctly, and stresses supply pipe running through or under a slab.
The effects are cumulative rather than immediate, which is why a backup or a leak often appears weeks after the storm rather than during it. People do not connect the two.
Uneven wetting makes it worse: water pouring off a roof onto one side of the house while the other stays dry produces differential movement, which is exactly what stresses pipe and foundations.
Which makes gutters and grading a plumbing issue, not just a landscaping one.
Before storm season
Most of this is drainage rather than plumbing, and that is the point — managing where the water goes prevents the plumbing consequences.
- Clear gutters and downspouts, and check the discharge lands well away from the foundation rather than at its base.
- Check the grade around the house slopes away from it. Soil settles over the years and quietly reverses.
- Locate your sewer cleanout and make sure it is accessible and not paved or planted over.
- Test any sump pump by pouring water into the pit, and check the discharge line runs clear and away.
- Know where the main water shutoff is, and confirm it turns.
- Deal with any drain that is already slow. A marginal line plus storm-season volume is where backups come from.
During and after
If a drain slows or a fixture gurgles during heavy rain, stop running water — including the dishwasher and washing machine, which discharge large volumes unattended. That alone often prevents a backup becoming a flood.
If water comes up through a floor drain or shower, treat it as contaminated. Keep people and pets off it, ventilate, and photograph before cleaning — many policies handle sewage backup differently from other water damage, and some require a specific endorsement.
Afterwards, walk the property. Look for new soft or sunken ground over the sewer route, water pooling where it did not before, and any drain that is now slower than it was.
Power matters too. If you are on a well, a power cut means no water at all — worth keeping some stored. And a sump pump is most likely to be needed in exactly the storm that takes the power out, which is the argument for a battery backup where a failure would be costly.