Most Likely Causes (Ranked)
The multiport valve on sand and DE filters uses a star-shaped spider gasket that seals between the valve ports. This gasket wears from rotation and chemical exposure over 5-10 years. When it fails, water leaks between ports — the most noticeable symptom is water running from the waste/backwash line while in filter mode. Replacement requires removing the valve from the filter.
Water trapped in outdoor pipes and equipment expands when frozen, cracking housings, pipes, and fittings.
Settling soil, root growth, and construction activity shift underground pipes and connections.
Metal components corrode from soil contact, water chemistry, and age. PVC degrades from UV if exposed.
Mowers, vehicles, foot traffic, and construction can damage above-ground and shallow-buried components.
How to Fix It
Replace Seal or Fitting
$5-25- 1Turn off water supply to the affected area.
- 2Remove and replace deteriorated seals, washers, or O-rings.
- 3Use Teflon tape on all threaded connections.
Repair or Replace Pipe Section
$15-100- 1Excavate if underground. Cut out damaged section.
- 2Replace with new pipe and appropriate connectors.
- 3Pressure test before burying.
Professional Repair
$200-1,000+- 1For underground main lines or complex pool plumbing.
- 2Leak detection may be needed first ($150-400).
- 3Get multiple quotes.
When to Call a Professional
Outdoor leaks waste water silently — check your water meter for unexplained usage.
Underground leaks can undermine foundations and cause sinkholes.
Pool leaks lose chemicals along with water, creating imbalanced and potentially unsafe water.
How to Prevent It
Winterize all outdoor plumbing before freezing weather.
Inspect visible outdoor plumbing seasonally.
Mark underground line locations before any digging.
Run the bucket test on pools monthly during season.
The Water Meter Test for Hidden Leaks
Turn off ALL water inside and outside. Read the meter. Wait 2 hours. Read again. Any change = leak somewhere in your system.
To isolate: shut off the main house valve. If meter still moves, the leak is between meter and house (underground). For irrigation: run each zone individually while watching for wet spots or pressure drops.
A single leaking sprinkler head wastes 12,000+ gallons per month — a $30-50 monthly water bill increase that's easy to miss.
Frequently Asked Questions
Check your water meter: turn off all indoor water, note the reading, wait 2 hours, read again. Any change = leak.
Professional leak detection uses acoustic equipment or thermal imaging ($150-400). DIY: look for wet spots, unusually green grass, or sinkholes.
Above-ground: $20-200 DIY. Underground: $200-2,000 professional.
Main water line from meter to house: some policies offer coverage. Irrigation and pool plumbing: typically not covered.