- Supply — pressurized water from the meter or well to every fixture, split into hot and cold at the water heater.
- Drain, waste, and vent — gravity carries used water out; vent pipes let air in so drains don't gurgle or siphon traps dry.
- Fixtures and appliances — toilets, sinks, tubs, the dishwasher, the washing machine, and the water heater.
Plumbing · Leak
| Project category | Plumbing |
|---|---|
| Problem type | Leak |
| Trade required | Plumbing |
| Urgency | Emergency — act now |
| Safety risk | High safety risk |
| DIY suitability | DIY for experienced homeowners |
| Cost category | Low cost |
| Typical timeline | Shut water off now; repair usually same or next day |
| Contractor type | Licensed plumber |
Repair option
Isolate at the shutoff, replace the failed component, and dry the cavity fully.
Replacement option
Repipe the run or the branch when corrosion is widespread.
Common causes
- Failed supply line or shutoff valve
- Worn washers, cartridges, or P-trap connections
- Pinhole corrosion in older copper
Relevant tools:emergency checklistdiy or hire a pro
Published September 4, 2026Last updated September 4, 2026
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Quick Answer
Plumbing problems are cheap when they're small and ruinous when they're ignored. The three things every homeowner should know: where the main shutoff is, how to read the water meter, and which symptoms mean shut it off right now rather than wait for a weekday appointment.
How the System Is Laid Out
Every house has three plumbing systems overlapping:
- Supply — pressurized water from the meter or well to every fixture, split into hot and cold at the water heater.
- Drain, waste, and vent — gravity carries used water out; vent pipes let air in so drains don't gurgle or siphon traps dry.
- Fixtures and appliances — toilets, sinks, tubs, the dishwasher, the washing machine, and the water heater.
Most emergencies are supply-side, because supply lines are pressurized 24 hours a day.
Find Your Shutoffs Today
- Main shutoff — usually where the supply enters the house, near the water heater, in a garage, or in a meter box near the street. Turn it fully off and back on once a year so it doesn't seize.
- Fixture stops — small valves under sinks and behind toilets. These let you isolate one fixture instead of the whole house.
- Water heater shutoff — on the cold inlet above the tank.
Tag them. Show everyone in the house. This single step is the highest-return thing in this guide.
The Ten-Minute Leak Test
- Turn off every fixture and appliance that uses water.
- Read the water meter, including the small leak-detection dial.
- Wait 30 minutes without using any water.
- Read it again.
Any movement means water is going somewhere it shouldn't. Combine that with an unexplained bill jump, a warm spot on a slab floor, or the sound of running water in a quiet house, and treat it as an active leak.
Symptoms and What They Usually Point To
| Symptom | Common causes | Urgency |
|---|---|---|
| Low pressure at one faucet | Clogged aerator or fixture stop | DIY |
| Low pressure whole house | Main valve, pressure regulator, corroded piping, leak | Same week |
| Toilet runs constantly | Flapper or fill valve | DIY |
| Slow drain in one fixture | Local clog or hair in the trap | DIY |
| Multiple drains slow at once | Main line blockage | Prompt |
| Sewage backing up | Main line blockage or failure | Call now |
| Water stain on ceiling below a bathroom | Supply or drain leak above | Prompt |
| Meter spinning with everything off | Hidden or slab leak | Shut off main, call now |
Maintenance That Prevents Big Bills
- Replace rubber washing-machine hoses with braided stainless every 5 years.
- Drain a few gallons from the water heater annually to reduce sediment.
- Keep hair catchers in showers rather than pouring chemicals down drains.
- In freezing weather, insulate exposed pipes and let a trickle run on exterior walls.
- Check under every sink twice a year — a flashlight and a dry paper towel find leaks early.
When to Stop and Call a Pro
Gas water heater work, sewer line work, repiping, and anything behind a wall belongs to a licensed plumber. Aerators, flappers, supply hoses, and a plunger are safely yours. If you can't stop water from entering a space, shut the main off first and call second.
Find a Pro Through Fixly Guide
If the next step is a professional, don't start with a phone book. Start with a diagnosis and a short list.
- Find a local pro — pick your trade and ZIP code to see vetted contractors serving your area.
- DIY or hire a pro? — a two-minute check that tells you which jobs are safe to handle yourself.
- Repair or replace? 12 expensive home decisions — how to judge a big-ticket quote.
- Home problem guides — start with the symptom, get likely causes and safety guidance.
- 15 house problems you shouldn't ignore — warning signs homeowners get used to.
Fixly Guide provides educational guidance only. Nothing here is a professional diagnosis or an inspection.
Fixly Project Decision Box
- DIY difficulty
- Moderate
- Estimated time
- 30 minutes – half a day
- Cost level
- Moderate
Main tools / materials
- Adjustable wrench
- Plunger or drain auger
- Bucket and towels
- Thread tape
When to stop and call a pro
- Water you cannot shut off at the fixture or main
- Sewage backing up into more than one fixture
- Water near electrical panels or outlets
- Gas water heater work beyond relighting a pilot
Need professional help?
Get a Licensed PlumberFrequently asked questions
Where is my main water shutoff valve?+
Usually where the water line enters the house — near the water heater, in a garage or basement, or in a meter box near the street. Find it and test it before an emergency.
How do I know if I have a hidden water leak?+
Shut off all water use, read the meter, wait 30 minutes and read again. Movement means water is escaping somewhere. Unexplained bill increases and warm spots on a slab floor are other signs.
Why is my water pressure low all of a sudden?+
A sudden whole-house drop usually points to a valve, the pressure regulator, or a supply-side problem such as a leak. Low pressure at a single fixture is almost always the aerator or its shutoff.
Are chemical drain cleaners safe to use?+
Repeated use can damage older pipes and makes a plumber’s job more hazardous. Mechanical clearing with a plunger or drain snake is generally the better first step.
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