A small plumbing leak rarely announces itself with a dramatic puddle. More often, it starts as a faint musty smell below a sink, a water bill that inches upward, or a cabinet floor that feels soft near a supply line. Knowing how to check plumbing leaks helps homeowners catch problems while the repair may be simple, rather than after moisture has damaged flooring, framing, insulation, or finishes.

For homebuyers, a basic leak check also adds useful context during a showing or final walk-through. It cannot replace a professional inspection, and hidden piping is not fully visible in any occupied home, but a careful look can reveal warning signs worth asking about before closing.

Start With the Water Meter

Your water meter is one of the most useful tools for finding a leak that is not visible. Choose a time when no one will need water for at least 30 minutes. Turn off faucets, avoid running the dishwasher or washing machine, and make sure sprinkler systems and ice makers are not operating.

Locate the meter, usually near the street or property line, and record the reading. Many meters also have a small leak indicator, often a triangle or gear-shaped dial, that moves when water is flowing. If the indicator moves while every water-using fixture is off, water may be leaking somewhere on the property.

Wait 30 minutes to two hours, then check the reading again. A change can point to a leak in a supply line, toilet, irrigation system, water heater connection, or another fixture. This test does not identify the exact source, but it tells you there is a reason to investigate further.

A meter test can be affected by systems homeowners forget about, including automatic irrigation, water softeners, whole-house filtration equipment, and refrigerator ice makers. If the meter moves, confirm those systems are not cycling before assuming a plumbing failure.

Check the Places Where Leaks Usually Begin

Most household plumbing leaks occur at connections, seals, valves, or fixtures that see frequent use. Begin indoors where the evidence is easiest to see.

Look Under Sinks and Around Appliances

Open the cabinets below kitchen, bathroom, laundry, and utility sinks. Use a flashlight and inspect the shutoff valves, supply hoses, drain trap, disposal connection, and the bottom of the cabinet. Run both hot and cold water for a minute, then look and feel carefully for drips or fresh moisture.

Pay attention to older valve stems and flexible supply hoses. Corrosion, green or white mineral buildup, rust, or staining around a connection can indicate a slow leak. A dry cabinet does not always mean the plumbing is sound, especially if a leak occurs only when the sink is draining or the dishwasher is operating.

Check behind the washing machine if access allows. Washing machine hoses are under pressure when the valves are open and can fail without much warning. Look for bulging, cracking, rusted fittings, or dampness at the connections. Also inspect the area around the water heater for water at the base, corrosion on piping, or a discharge pipe that appears to be dripping.

Test Toilets for Silent Leaks

A leaking toilet is common, often quiet, and easy to miss. Remove the tank lid and listen for periodic refilling when the toilet has not been flushed. Then add several drops of food coloring to the tank water. Do not flush.

After 10 to 15 minutes, check the bowl. If colored water has entered the bowl, the flapper or another tank component is allowing water to pass through. This can waste a significant amount of water over time, even though there is no leak on the bathroom floor.

Also check around the toilet base. A loose toilet, stained flooring, recurring odor, or moisture around the base may point to a failed wax ring or another issue below the fixture. Do not simply caulk over suspicious staining or movement. The source should be identified first.

Run Fixtures One at a Time

Turn on each faucet, shower, and tub. Watch for drips at the spout, leaking handles, loose showerheads, or water escaping around trim plates. Then stop the water and watch the drain area beneath the fixture if it is accessible.

For tubs and showers, look at nearby ceilings and walls, especially on the level below. Peeling paint, a brown ring, bubbling drywall, or a patch that feels soft can indicate water escaping from a drain, overflow, supply connection, or shower enclosure. Because showers are used intermittently, the damage may be visible long before active moisture is easy to find.

Know the Difference Between a Supply Leak and a Drain Leak

The timing of moisture can provide an important clue. A supply leak can occur whenever pressurized water is available, even when no fixture is running. It may show up as meter movement, persistent dampness, or a steady drip at a valve or pipe connection.

A drain leak usually appears only after water is used. For example, water under a bathroom sink that appears after filling and draining the basin is more likely related to the drain assembly than the supply lines. A ceiling stain below a shower that worsens after use may involve the shower drain, tub overflow, enclosure, or plumbing inside the wall.

This distinction is helpful, but it is not a diagnosis. Water can travel along pipes, framing, and subflooring before becoming visible. The wet spot is not always directly below the leak.

Inspect Outside Plumbing and the Home’s Exterior

Outdoor spigots, irrigation components, and exterior walls deserve the same attention as indoor fixtures. Turn on each hose bib and check for drips at the handle, connection, and wall penetration. In Southwest Washington, repeated wet weather can make exterior moisture clues harder to interpret, so look for patterns rather than one damp area after rain.

Check beneath exterior faucets inside the home when accessible, particularly in crawlspaces, garages, or utility areas. Look for wet insulation, dripping pipes, standing water, or wood staining. If a hose bib is frost-damaged, it may leak inside the wall only when the exterior faucet is turned on.

Walk the property and watch for unusually green patches of lawn, soggy soil during dry weather, or pooling near a water line. These conditions may indicate an underground water leak, though poor drainage and irrigation problems can create similar symptoms. A moving water meter with no interior source increases the need for professional evaluation.

Watch for Indirect Warning Signs

Not every plumbing leak is visible. Changes in the home can provide early evidence of hidden moisture:

• A musty odor in a bathroom, laundry room, cabinet, crawlspace, or basement
• New water stains, bubbling paint, warped trim, or damaged flooring
• A sudden or unexplained increase in the water bill
• Reduced water pressure at one fixture or throughout the home
• Mold growth where condensation is not normally expected
• A water heater that runs frequently or shows corrosion around connections

These signs do not always mean there is an active plumbing leak. A roof leak, exterior water intrusion, condensation, or drainage issue can produce similar damage. That is why a methodical inspection matters: the goal is to identify the likely source, not to guess based on one symptom.

When a DIY Check Is Not Enough

Turn off the water supply and contact a qualified plumber promptly if you find active leaking near electrical components, a burst hose, water coming through a ceiling, sewage backup, or significant water around a water heater. Fast action can reduce damage, but avoid opening walls or making repairs that could hide evidence before the cause is understood.

For buyers, a general home inspection provides a visual assessment of accessible plumbing components, fixtures, and signs of leakage at the time of inspection. It is not a guarantee against concealed defects or future failures. When there are concerns about buried drain lines, slow drains, older sewer systems, or recurring backups, a sewer scope can provide information a standard visual inspection cannot.

ProView360 Home Inspection helps clients understand visible plumbing conditions in clear, photo-supported terms, so concerns can be addressed with the right next step instead of assumptions. If a condition needs further evaluation, the most useful question is often not “Is this a leak?” but “Where is the water coming from, and what has it affected?”

A five-minute check under a sink may save a cabinet. A careful meter test may uncover a problem before a utility bill does. Build these checks into seasonal home maintenance, and treat new stains, odors, or changes in water use as a reason to look closer rather than something to watch indefinitely.