Older Wilmington Homes: The Plumbing That Goes First

The short answer

In an older Wilmington house, the plumbing that usually goes first is the original metal: galvanized steel supply pipe that has rusted and narrowed from the inside, cast iron drain stacks and horizontal runs that have scaled or thinned, and the buried water and sewer lines between the house and the street, which the property owner is responsible for maintaining.

That list follows from the age of the city’s housing, which is materially older than the rest of New Castle County. If you need plumbing service in Wilmington today, Spangler Plumbing runs 24/7 across northern New Castle County.

Why housing age changes the plumbing conversation in Wilmington

According to the U.S. Census Bureau’s 2019–2023 American Community Survey 5-year estimates, 43.4% of Wilmington’s 35,772 housing units were built in 1939 or earlier, and another 11.8% in the 1940s, so 55.2% of the city’s housing predates 1950 (U.S. Census Bureau, ACS 2019–2023 5-year, table DP04, Wilmington city, Delaware).

The county looks very different. The same table for New Castle County shows 10.8% of housing built in 1939 or earlier and 5.6% in the 1940s: about one home in six predates 1950, against more than one in two inside the city (U.S. Census Bureau, ACS 2019–2023 5-year, table DP04, New Castle County, Delaware). The median year built says it in one number: 1946 for Wilmington city, 1975 for New Castle County, 1986 for Delaware (U.S. Census Bureau, ACS 2019–2023 5-year, table B25035).

Age alone does not break plumbing. The original materials of those eras fail in known ways, and a house this old has usually had at least one partial repipe, so the trouble tends to start where one era’s pipe meets the next.

Supply pipe: what was installed when

Supply pipe is the system most likely to have been partly replaced already, and to still have an original run hiding in a wall.

Galvanized steel. Threaded, zinc-coated steel was the standard supply pipe for the pre-war and mid-century decades. It rusts from the inside, so the classic symptoms are weak flow at the fixture farthest from the meter, brown water after the house has sat unused, and threaded joints that weep. The EPA also notes that lead particles can attach to the surface of galvanized pipe and, over time, enter the drinking water (U.S. Environmental Protection Agency). Wilmington’s service line inventory carries a category called “galvanized requiring replacement” for that reason (Wilmington Water, Service Line Inventory).

Copper with lead solder. Most Wilmington houses repiped between the 1950s and the 1980s got copper, which is durable. The joints are the question: the EPA states that solder made or installed before 1986 contained high lead levels (U.S. Environmental Protection Agency), and Wilmington Water notes that homes built after 1988 are less likely to have fixtures or solder containing lead (Wilmington Water, Lead Reduction Program).

Polybutylene. Only about 8% of the city’s housing dates from the 1980s and 1990s, the polybutylene era (U.S. Census Bureau, ACS 2019–2023 5-year, table DP04). If that is your house, see how to identify polybutylene pipes.

On lead, the facts and nothing more. Wilmington Water states that lead does not exist in the water leaving its treatment plant or in its mains, that it uses corrosion control treatment, and that where lead turns up it comes from service lines or in-home plumbing in older homes (Wilmington Water, Lead Reduction Program). The City’s service line inventory is live, and the City replaces lead service lines from the main to the meter at no cost during scheduled water main projects, with a subsidy for the privately owned curb-to-meter portion elsewhere (Wilmington Water, Lead Service Line Replacement).

Drain and waste: the older-house failure pattern

Drain piping fails slowly. In a pre-1960 Wilmington house it is almost always cast iron, sometimes with galvanized steel branch lines.

Cast iron is genuinely durable. The Cast Iron Soil Pipe Institute’s handbook explains that when cast iron corrodes it leaves a dense, adherent graphitic layer that acts as a barrier against further corrosion (Cast Iron Soil Pipe Institute, Cast Iron Soil Pipe and Fittings Handbook). That layer is also rough, and roughness catches grease, hair, and paper. So the old-house failure is rarely a sudden break. It is a drain that clears with a snake, runs fine for a few months, then slows again, because the bore has scaled down to a fraction of its original size.

The same handbook notes that internal corrosion is accelerated by strong acids at a pH of 4.3 or lower left in contact with the pipe for an extended period, a good reason not to pour aggressive chemical openers down an old stack every time it slows, and that joining different metals, such as iron to copper or brass, can set up galvanic corrosion (CISPI Handbook).

One slow bathroom sink is usually a trap or branch line. Several fixtures on one floor slowing together, gurgling in one drain when another runs, or a new sewer smell in the basement point at the main stack or the run under the slab. That is when a camera inspection earns its keep: it shows whether drain cleaning will fix it or a section of pipe has thinned through and needs replacing.

The buried lines between the house and the street

Inside city limits, water and sewer service comes from the City itself, through the Department of Public Works operating as Wilmington Water. According to the City’s customer responsibility page, the customer is responsible for “addressing any water leaks and plumbing issues within your property, including the water pipes connecting your home to the city’s water main,” and for “maintaining and repairing, if necessary, the sanitary and storm sewer lateral lines from your property to the main sewer line” (Wilmington Water, Customer Responsibility). The City adds that standard homeowners’ insurance policies typically do not cover those repairs (Wilmington Water, Service Line Protection Plans). Read that as the City’s description of its own rules, not legal advice.

For a house built before 1950, the buried water service is often the last piece of original pipe left. Wilmington Water’s FAQ lists the materials it finds in service lines as copper, galvanized iron, lead, or plastic (Wilmington Water, FAQ). The sewer lateral from the same era is typically cast iron near the house and cast iron or clay out to the main, and clay is jointed every few feet, which is where roots get in. The tells are a soft green patch of lawn in August, or a floor drain that backs up when it rains. To check your own service line, the EPA’s Protect Your Tap guide is a step-by-step walkthrough, and the City’s inventory map shows what it has on record for your address.

One more local item: the City runs a cross-connection and backflow control program. Its contractor, HydroCorp, sends letters when a survey is due, and some backflow prevention assemblies must be tested by a certified tester on installation, relocation, repair, and annually; the examples given include lawn sprinkler systems, pools, and boilers (Wilmington Water, Cross Connection and Backflow Control Program). If you get one of those letters, it is real.

What is worth doing now and what can wait

Do now:

• Find your main shutoff and make sure it turns. If it is an original gate valve that will not close fully, replace it before an emergency.
• Look up your address on the City’s service line inventory map. If it says lead, galvanized, or unknown, follow the City’s lead program guidance.
• Get a camera inspection of the main drain and lateral if you have had more than one backup or slow-drain call in a year, or if you are buying. It answers the question the snake cannot: buildup or broken pipe.
• Stop using acidic chemical openers on cast iron. Clear it mechanically, and if a drain keeps coming back, find out why.

Plan for:

• Replacing whatever galvanized supply pipe remains. A partial repipe that ties new copper or PEX into old steel leaves the steel as the weak point and the transition as a corrosion site.
• A staged replacement of the cast iron stack if inspection shows it has thinned through. A stack that scans intact can run for years.

Leave alone:

• Sound copper with pre-1986 solder. It is not a reason to repipe by itself; if you want to know whether lead is present at the tap, both the City and the EPA say to test the water.
• Cast iron that scans scaled but intact. Clean it and re-scan later.

For whether a given problem can wait until morning, what counts as a plumbing emergency lays out the triage.

Questions Wilmington homeowners ask

How old is the average house in Wilmington, Delaware?

The Census Bureau’s 2019–2023 ACS estimates put the median year built at 1946 for Wilmington city, against 1975 for New Castle County. About 43% of the city’s housing was built in 1939 or earlier, and more than half before 1950.

Who is responsible for the water line from the street to my house in Wilmington?

According to Wilmington Water’s customer responsibility page, the customer is responsible for the water pipes connecting the home to the City’s main and for the sewer laterals out to the main sewer line. The City’s lead program is the exception, replacing lead lines from the main to the meter during scheduled main projects.

Does my old Wilmington house have lead pipes?

Not necessarily. Wilmington Water says homes built before 1988 are more likely to have lead service lines, pipes, or solder, but the only way to know is to check the City’s service line inventory map and, for certainty, test your water.

Should I replace galvanized pipe before it leaks?

Usually it is worth planning for. Galvanized steel corrodes from the inside, and the EPA notes that lead particles can attach to its surface. A plumber can tell you how much remains and where it meets newer pipe.

What is the backflow letter I received from the City of Wilmington?

The City’s cross-connection and backflow control program, run through HydroCorp, sends letters when a survey or test is due. Some assemblies must be tested by a certified tester annually and after installation or repair; the City’s program page explains who to contact.

Get the old house looked at before it decides for you

Most of what goes wrong in a pre-war Wilmington house announces itself first: a drain that keeps slowing, a valve that will not turn, a soft patch in the yard. That is the moment to have someone look, while the fix is still a choice. Spangler Plumbing, a Delaware Master Plumber (license UT1488), provides plumbing service in Wilmington and across northern New Castle County, 24/7. To have what is left of the original pipe assessed, get in touch and tell us what the house has been doing.