Small leaks add up fast. The EPA's WaterSense program estimates that the average household's leaks waste more than 9,300 gallons of water a year, and that nine percent of homes have leaks wasting 50 gallons or more every day (EPA WaterSense). A lot of that comes from leaks people can fix themselves. The rest comes from the kind of problems below.

Here are seven plumbing problems that call for a licensed plumber, how to spot each one, and what to do in the minutes before help arrives.

The 7 problems

1. Hidden leaks and slab leaks

A slab leak is a broken water line under your home's concrete foundation. You rarely see the water itself. You see what it does: a water bill that jumps for no reason, a warm spot on the floor, the sound of running water when every tap is off, or a water meter that keeps turning when nothing in the house is in use.

Finding the break takes acoustic and electronic leak detection gear, and fixing it may mean rerouting the line rather than breaking open the slab. Guesswork here means tearing up floors in the wrong place.

What to do first: turn off every fixture and watch the meter for a few minutes. If it moves, close the main shut-off valve and call a plumber.

2. A water heater that leaks, rumbles or quits

Popping or rumbling from the tank, rusty hot water, water pooling at the base, or no hot water at all are the classic signs. In hard-water areas these show up sooner. Santa Ana, for one, reports tap water hardness of about 250 ppm (City of Santa Ana), and that mineral scale settles at the bottom of the tank and coats tankless heat exchangers.

A water heater combines water pressure, high heat and, often, a gas connection. Replacements in California also have to be strapped against earthquake motion under Health and Safety Code §19211, and they usually need a permit. A flush or descale every year keeps scale from shortening the unit's life. If you're dealing with hard water at home, The 5 Star Plumbing provides plumbing services in Orange County  and Los Angeles that cover water heater repair, tank flushes and tankless descaling.

What to do first: for a leaking tank, set the gas control to Off or Pilot (or switch off the breaker on an electric unit), then close the cold-water valve on top.

3. The smell of gas

A rotten-egg smell near the stove, dryer or water heater, a hissing sound near a gas line, or dead plants along a buried line can all point to a gas leak. This is the one problem on the list that is a safety emergency first and a plumbing job second.

Gas line repair has to be done by a licensed professional, pressure-tested and, in most cities, permitted and inspected.

What to do first: don't flip switches, light anything or use your phone inside. Get everyone out, then call your gas utility or 911 from outside. In most of Southern California that's SoCalGas at 1-800-427-2200. Book the repair once the utility says it's safe.

4. Low water pressure across the whole house

Weak pressure at one faucet is usually a clogged aerator. Weak pressure everywhere, often with rusty or discolored water, points to something bigger: corroded galvanized pipes, a hidden leak, or a failed pressure regulator.

Older homes are the usual suspects. Galvanized steel pipe rusts from the inside, narrowing until little water gets through. The long-term fix is often a partial or whole-house repipe, which means opening walls, sizing new lines and passing an inspection.

What to do first: check that the main shut-off is fully open, then test pressure with a hose-bib gauge (sold at hardware stores for a few dollars). Note the reading for your plumber.

5. Several drains backing up at once

One slow sink is a local clog. When the toilet gurgles as the washing machine drains, or water comes up in the shower when you flush, the problem is in the main sewer line. Tree roots, grease build-up and cracked or sagging clay and cast-iron pipe are the common causes.

Renting a drain snake can push through a root mass without fixing it, and it tells you nothing about the pipe's condition. A plumber will run a camera down the line to see what failed before quoting the repair. Target Plumbing Services, for example, inspects the line on camera first so homeowners pay to fix only the section that actually broke.

What to do first: stop using water in the house. Every flush and load of laundry adds to what's backing up.

6. Water pressure that's too high

Banging pipes when a valve shuts (called water hammer), faucets that spray, a toilet that keeps refilling and relief valves that drip are signs the pressure is too high. It sounds harmless, but it wears out supply lines, valves and appliance hoses early.

The California Plumbing Code requires a pressure regulator when static pressure exceeds 80 psi, and these regulators wear out over time. The City of San Diego notes that a sudden pressure increase most often comes from a faulty regulator on the property. Replacing or resetting one is a job for a plumber.

What to do first: test with a hose-bib gauge. Anything above 80 psi is worth a service call.

7. Drains that keep clogging after you clear them

A drain that clears with a plunger and clogs again a week later is telling you something. Grease, soap and mineral scale coat the inside of the pipe, and each clearing only punches a small hole through the build-up.

Hydro jetting uses high-pressure water to scour the full width of the pipe. It works well, but on old or damaged pipe it can do harm, so a plumber should check the line before jetting it.

What to do first: skip the chemical drain cleaners. They rarely clear a full blockage, and they can damage older pipes and anyone working on them later.

How to pick the right plumber

The right plumber makes a big job feel routine. A few checks before you hire save a lot of trouble later.

• Check the license. In California you can look up any contractor's license number at cslb.ca.gov. Unlicensed workers may only take jobs under $1,000 that need no permit and that they do alone (CSLB). Every problem on this list is bigger than that.
• Ask for a written price before work starts. A flat price for the whole job is easier to compare than an open-ended hourly rate.
• Ask how they'll diagnose it. For sewer, slab and pressure problems, a good plumber tests or inspects before quoting.
• Ask about permits. Water heaters, repipes, sewer replacements and gas work usually need one. The plumber should pull it.
• Get the warranty in writing. Know what's covered and for how long.
• For emergencies, ask who answers the phone. A real dispatcher at 2 a.m. matters more than a fast website.

Frequently asked questions

Can I fix a slab leak myself? No. Finding a leak under concrete takes specialized detection equipment, and the repair often means rerouting a pipe or opening the slab in exactly the right spot.

How do I know if a clog is in the main sewer line? If more than one drain is slow or backing up at the same time, or one fixture gurgles when another drains, the clog is most likely in the main line.

What water pressure is normal for a house? Most homes run comfortably between 40 and 80 psi. The California Plumbing Code requires a pressure regulator when static pressure is above 80 psi.

How often should a water heater be flushed? Once a year is a good habit, and more often in hard-water areas. Tankless units need descaling on a similar schedule.

The bottom line

A dripping faucet can wait for the weekend. A spinning water meter, a gas smell, sewage in the tub or a tank leaking at the base can't. Learn where your main water shut-off and gas valve are today, so you can act fast when one of these problems shows up. Then call a licensed plumber who will find the cause, explain it in plain words and put the price in writing before the work begins.