As a plumber, I’ve learned that some of the most expensive issues in a rental property aren’t visible during a showing!

I have compiled a list of 10 plumbing red flags worth paying attention to whenever evaluating an investment property.

1. Cast Iron Drain Lines

Warning Signs:

• Home built before the 1980s

• Frequent drain backups

• Rust flakes in cleanout

• Visible corrosion

Likely Outcome:

• Recurring drain issues

• Sectional repairs or full sewer replacement

• Unexpected capital expenses

2. Polybutylene Water Lines

Warning Signs:

• Gray plastic water piping

• Homes built between 1978–1995

• Prior leak repairs

Likely Outcome:

• Increased risk of pipe failures

• Water damage claims

• Future repipe project

3. History of Frequent Drain Cleaning

Warning Signs:

• Seller mentions routine snaking

• Multiple plumbing invoices

• Slow drains despite recent cleaning

Likely Outcome:

• Root intrusion

• Sewer belly

• Damaged or offset sewer pipe

4. Large Trees Near Sewer Route

Warning Signs:

• Mature trees between house and street

• Previous root treatments

• Slow draining fixtures

Likely Outcome:

• Root intrusion

• Recurring backups

• Sewer repairs or replacement

5. Low Water Pressure

Warning Signs:

• Weak flow at multiple fixtures

• Older galvanized piping

• Pressure fluctuations

Likely Outcome:

• Pipe replacement

• Pressure regulator replacement

• Hidden plumbing deficiencies

6. Evidence of Previous Water Damage

Warning Signs:

• Ceiling stains

• Fresh paint patches

• Warped flooring

• Cabinet damage under sinks

Likely Outcome:

• Active plumbing leaks

• Mold concerns

• Additional repair costs beyond plumbing

7. Aging Water Heater

Warning Signs:

• Unit over 10 years old

• Rust around base

• Corrosion on connections

• Inconsistent hot water

Likely Outcome:

• Near-term replacement

• Emergency service calls

• Potential water damage from failure

8. Poor Drainage Around the Property 

 

Warning Signs:

• Standing water after rain

• Downspouts discharging near the foundation

• Erosion around the home

• Soggy crawlspaces

Likely Outcome:

• Foundation settlement

• Sewer line bellies caused by soil movement

• Water intrusion into basements or crawlspaces

9. No Sewer Scope Performed

Warning Signs:

• Older property

• Large trees on lot

• Unknown sewer history

• Standard inspection only

Likely Outcome:

• Hidden sewer defects

• Major repair costs discovered after closing

• Reduced cash flow from unexpected expenses

10. Long-Term Vacant Property

Warning Signs:

• Property vacant for months

• Utilities recently turned back on

• Little evidence of recent occupancy

Likely Outcome:

• Hidden leaks

• Failed shutoff valves

• Drainage issues

• Plumbing failures shortly after move-in

Bottom Line

Most investors focus on roofs, HVAC systems, and cosmetic updates. In my experience, some of the most expensive surprises are underground or hidden behind walls.

A few hundred dollars spent on plumbing due diligence can potentially save thousands after closing.