Plumbing 101: What Every Arcadia Homeowner Should Know (And When to Call a Pro)

Plumbing is one of those things that runs quietly in the background of your home for years, and then one day it absolutely does not. A slow drip under the sink. A shower that’s suddenly not draining. Or the worst: a wet ceiling where there definitely should not be a wet ceiling.

As a general contractor working across Arcadia and the San Marino area, I open walls on a regular basis. What I find inside them tells a story. Some of the homes we work on have original 1950s copper lines that are still going strong. Others have galvanized pipe that was overdue for replacement twenty years ago. A lot of the older SGV housing stock is in that in-between zone where everything looks fine until you look closer.

This post is not a DIY plumbing manual. It’s the orientation that I wish every homeowner had before they either ignored a problem too long or attempted something they shouldn’t have. Know your system, know the limits, know when to call.

How Your Home Plumbing Actually Works

Your home has two separate plumbing systems that serve completely different purposes and should never cross.

The supply system brings pressurized fresh water into your home. It comes in from the municipal main at the street, passes through your main shutoff valve, your water meter, and then branches throughout the house to feed every faucet, toilet, dishwasher, washing machine, and water heater. In most SGV homes built before the 1980s, supply lines are copper. Homes built more recently may have CPVC or PEX, which is more flexible and easier to work with. If you have galvanized steel supply lines, that’s something worth knowing about and addressing proactively.

The drain, waste, and vent (DWV) system takes wastewater out. Everything drains by gravity into progressively larger pipes that eventually connect to the city sewer main at the street. The vent part of that system is often overlooked: those pipes going up through your roof exist to let air into the drain lines so water can flow freely and sewer gases can escape to the outside rather than backing up into your house. A gurgling toilet or a drain that smells like a sewer almost always points to a vent issue.

Every fixture in your house also has a P-trap: that curved section of pipe under your sink. It holds a small amount of water that acts as a seal, preventing sewer gas from coming back up through the drain. If you have a drain that smells bad but doesn’t seem blocked, run water into it. A trap that has dried out from disuse is often the cause.

What Homeowners Can Safely Do Themselves

I’m not going to tell you that you need a contractor for everything. Some plumbing tasks are genuinely accessible to a careful homeowner with basic tools. Here is what falls into that category.

Replacing a faucet or showerhead. This is a legitimate DIY job. Turn off the water supply at the valves under the sink (or at the main if there are no local shutoffs). Remove the old fixture. Install the new one following the manufacturer instructions. Turn the water back on slowly and check for leaks at every connection. Take your time and use plumber’s tape on any threaded fittings.

Replacing a toilet flapper or fill valve. Most toilet running issues are a bad flapper or a failing fill valve. Both are $10-15 parts at any hardware store, and the replacement is straightforward. The flapper is the rubber seal at the bottom of the tank. If your toilet runs between flushes, that’s usually the first thing to replace.

Clearing a slow drain. A drain snake or a cup plunger can clear most clogs in a sink or tub. Use a drain snake rather than chemical drain cleaners if you can: the chemicals are hard on older pipes and only sometimes effective. For a toilet, use a flange plunger, not a cup plunger. The shape matters.

Replacing a P-trap. The curved pipe under your bathroom or kitchen sink can be replaced without soldering or special tools. It’s hand-tight slip fittings in most cases. Just make sure you have a bucket underneath before you start.

Replacing a toilet. This one intimidates people but is manageable. The water supply line and the wax ring at the floor are the two connections. Take photos before you disconnect anything. Buy a new wax ring and supply line whenever you install a toilet, even if the old ones look okay.

Where the Line Is: What Requires a Licensed Plumber (and Usually a Permit)

In California, and specifically in Arcadia and Los Angeles County, any work that changes the plumbing system beyond repair or direct replacement of existing fixtures generally requires a permit and a licensed plumber. This includes:

• Relocating or adding supply or drain lines. If you are moving a sink, adding a bathroom, or changing the layout of a kitchen remodel, the rough plumbing needs to be permitted and inspected. This is not optional. It is also genuinely complicated work that involves cutting into existing lines, maintaining proper drain slope, and tying into vents correctly.
• Water heater replacement. This requires a permit in most California jurisdictions. The installation also has specific requirements for seismic strapping, pressure relief valve discharge, and gas line work. A plumber who pulls a permit will do all of this correctly. One who does it without a permit probably will not.
• Repipe or partial repipe. If you have galvanized supply lines, the right move is a full repipe to copper or PEX. This is major work that opens walls and requires inspection. It should be done by a licensed plumber with a permit.
• Gas line work. This is not plumbing in the traditional sense, but licensed plumbers often do gas line work. Any new gas line, extension, or modification to a gas appliance connection requires a permit. I cannot stress enough that this is not a DIY category. Natural gas leaks cause fires and explosions. Pull the permit. Get the inspection.
• Sewer line work. Any work on the sewer lateral — the pipe that runs from your house to the city main — requires a permit. Given what’s at stake if this fails, this is also work you want done correctly the first time.

Red Flags: Situations That Need Immediate Attention

There are a few plumbing situations that warrant fast action. Not "I'll get to it this weekend" — actual immediate action.

Water stains on ceilings or walls. This is active water damage, and it is almost always worse than it looks from the surface. A stain on a ceiling typically means a fixture or pipe above it has been leaking long enough to saturate the structure. The visible stain represents a fraction of the wet material behind it. This does not get better on its own. The longer it goes, the more likely you are dealing with mold and structural damage, not just a stain.

A drop in water pressure throughout the house. If pressure has dropped across multiple fixtures at the same time, that points to a main line issue, a failing pressure regulator, or the early stages of a significant leak. A single low-pressure fixture is usually a clogged aerator or valve issue. All fixtures low at once is something different.

Sewage smell inside the house. This means sewer gas is getting in somewhere it shouldn’t. The causes range from a dried P-trap (run water into unused drains) to a cracked or deteriorated wax ring under a toilet to a broken sewer line under the slab. The first two are easy fixes. The third is not, but it matters because sewer gas includes methane and hydrogen sulfide, which are both combustible and toxic at high concentrations.

Discolored water. Brown or rusty water from a cold tap usually indicates pipe corrosion. If you have galvanized steel supply lines, this is a strong signal to have your system evaluated. Discolored water from the hot tap only can sometimes be a water heater issue. Either way, it should not be ignored.

Water pooling in the yard with no explanation. This is often a sign of a sewer line leak underground. Tree roots are a common cause in older neighborhoods — a root can infiltrate and eventually collapse a clay sewer line. A camera scope of the sewer line costs a few hundred dollars and tells you exactly what you are dealing with before you commit to any repairs.

Plumbing and Remodels: What to Plan For

If you are doing a bathroom remodel or kitchen renovation, the plumbing rough-in phase is the time to address anything that has been on your list for years. Once the walls are open and the fixtures are out, the incremental cost of replacing aging supply valves, upgrading drain lines, or adding a second shutoff is relatively small. Those same upgrades after a remodel is finished will cost significantly more because they require reopening finished work.

Things worth doing during a remodel while the walls are open:

• Replace all stop valves under sinks and toilets if they are original to the house
• Add individual shutoffs to fixtures that do not currently have them
• Upgrade to PEX supply lines if you have galvanized or original copper that is showing age
• Install an accessible cleanout on the drain lines if one does not already exist
• Verify drain slope — it should be 1/4 inch per foot minimum

We handle the full scope of plumbing rough-in and finish work as part of our remodel projects, and we coordinate all inspections. You should not have to manage that piece separately. For more on what a remodel project actually involves from start to finish, see our post on what to expect during a bathroom remodel, week by week.

Plumbing is not glamorous but it is foundational. A house with great finishes and failing plumbing is a liability, not an asset. Understanding what you have, maintaining it honestly, and addressing problems before they become emergencies is how you protect both the home and your budget over the long run. For a broader look at preparing for a renovation, see our guide on 10 things every SGV homeowner should know before starting a remodel.