Plumbing System Overview

Home inspection outside tap hose bib

Hot and cold running water has become so common in our homes that we can take for granted the incredible feats of engineering and technology that have made this modern convenience possible. For Home Inspectors, the plumbing system of a home can be a common place to discover deficiencies during a home inspection and because of life safety concerns with sewer gases, only licensed Plumbers should make changes to a plumbing system.


Water Source

For most urban homes, the question of water source is not a concern as the municipality or local water utility deliver water to the property line. However, even this water had to be sourced from somewhere and for many communities, finding enough water for our insatiable demand is a challenge.


Water can be sourced from ground water like at lakes and rivers, or it can be sourced underground from wells and aquifers (underwater rivers). Often, to ensure enough water during the dry seasons, surface water will be stored using dams and reservoirs. The term watershed is used to describe the land area from which surface water run off comes to the water source. It is important that this watershed be free of pollutants or even natural contaminants so the water is safe for drinking.


Drinking water nearly always needs to be treated in order to be safe. Even runoff from natural sources can carry with it bacteria that can make people very sick. This role is carried out by the local water utility and can use processes like ultraviolet light and adding small amounts of chlorine to make the water system safe.


Once the water has been treated, the utility uses a series of pipes, often laid under the road network, to deliver water to businesses and homes. In order for water to flow along the piping, the utility needs to maintain a pressure in the system that is high enough to reach multi-story buildings or be used for firefighting. This is achieved typically with gravity by raising water with pumps to higher ground or using water towers to store water at a higher elevation. Once the water is higher than the community, gravity will create water pressure needed for delivery. In some cases water pressure is created through the use of local pumps however this risks water not being available in a power outage or pump failure.


Water piping has been an area of major concern for some older communities. Original piping may have been anything from hollowed out logs to lead or copper pipes which could leach contaminants into the water supply. Today, most municipalities are installing high pressure plastic water piping systems. While this piping system is important to the home, it is outside the scope of a home inspection.


Many rural homes do not have access to a communal water supply and need to rely on either trucked in water or private well systems. Ensuring water is safe for drinking and in plentiful supply requires expert knowledge and testing in a lab which is why home inspectors always need to refer home buyers to experts when a well or private system is involved. 


Water Supply Pipes

Water is transferred by the local water utility to the property line of the home where the homeowner then becomes responsible for the connection to the house itself. Commonly, at the property line there is a valve which can be turned on or off using a special water 'key' (a long rod with a special end). In the event of a catastrophic water system problem at the home, this valve isolates the entire property from the utility system.


The water supply pipe to the home is important to home owners for 4 reasons:

  1. Failures - Any failure of the pipe on the property from mechanical damage like shovels, vegetation like tree roots, or deterioration from age is the responsibility of the home owner. Unfortunately, as the line is buried, leaks or deterioration may not be noticed until there is a major problem. Small leaks over time can erode soil underground creating sinkholes or may be the source of water leaking into basement cracks.
  2. Water Supply Level - The amount of available water to the home is largely dependent on the size of pipe coming to the home. A newer 3/4" pipe, thanks to the increased surface area and reduced pressure losses, can carry 3 or more times the amount of water than an older 1/2" pipe could carry. This is particularly important when a home may have a basement suite added.
  3. In-Home Emergency Turn off - In addition to the utility shut off at the street, homes have an emergency water turn off at the supply pipe connection. In the event of an in-home water leak, this valve can turn off water and allow for maintenance. Identifying the location of this shut off is part of a standard home inspection.
  4. Pressure Reducing Valve - While this is technically after the supply pipe to the home, the Pressure Reducing Valve (PRV) takes the high pressure utility water and lowers it for domestic use. Utility water pressures can be in the hundreds of pounds per square inch (psi) while domestic taps and appliances are typically rated to a maximum if 80psi.


In condo's, the utility still delivers water to the property line where it becomes the responsibility of the strata to deliver the domestic water to each strata unit. Commonly, water turn offs still exist in each suite however the suite owner is usually only responsible for the water supply inside the unit itself.


Supply Water Distribution

There are many water pipes in a home. Supply pipes carry hot and cold domestic water, heating pipes may carry hot water from the heating system, fire sprinkler systems (rare in houses) may have high pressure water on standby, and drain pipes carry used water safely away. Supply water refers to the pressured domestic use water from the utility that makes its way to all the taps and appliances in the home.


Supply piping in homes is an area of concern as it is constantly under pressure and any failure or deterioration of the system will result in leaks and floods causing potentially expensive damage. This is one of the reasons why only licensed Plumbers should make changes to the plumbing in our homes.


Water supply pipes in homes have been made out of many materials in the last century. The most common being:

  • Legacy Piping Systems - Homes built pre-1950's may have used lead or galvanized steel pipes. These pipes have commonly been replaced due to deterioration in the last few decades and if a home inspector sees them today they will recommend they be replaced for safety reasons and as they are past their expected life spans.
  • Copper - Copper piping was in common use for most of the 1900's. Copper life spans can vary based on the thickness of the pipes, the minerals in the water, and even the water temperature. Copper pipes over 30 years old have been known to develop pin hole leaks which may be a sign of premature system deterioration however in ideal conditions copper can last over 100 years.
  • Polybutylene (PB) Plastic - When copper prices first spiked in the 80's, home builders looked for more affordable supply pipe alternatives. Polybutylene piping was marketed as the piping of the future however cases of premature failure in the fittings erupted in many class action lawsuits causing the Polybutylene industry to shut down. PB piping is usually blue-grey in colour and very common in homes built in the 90's. Home inspectors highlight PB piping as a concern in a home inspection because of the higher risk for leaks.
  • PEX Plastic Piping - While in North America Polybutylene was being marketed, Europe was using a plastic piping made of cross-linked polyethylene commonly called PEX. With the failure of PB in North America and copper prices still high, North American suppliers started to supply PEX in the late 1900's and early 2000's. While it is the newest material in common use, PEX has not demonstrated premature failure issues. Builders like PEX as it comes in rolls, bends around corners, and does not require soldering connections which all saves labour time and material costs.


Supply pipes in the home bring water to the various sinks, fixtures, and water using appliances in the home where there is a shut off valve and connector for the fixture. The final connections for most fixtures and appliances use small connector pipes which are often integrated in by the fixtures manufacturers.


Hot Water

Local water utilities (or private wells) only provide a source of 'cold', or ground temperature, water. In order to provide hot water to our taps and appliances, our homes need a water heating appliance, typically fuelled with electricity or natural gas, to heat the 'cold' water supply and create a domestic hot water line. The connection to the cold water supply provides the hot water pressure and replacement water as hot water is consumed.


Common hot water heating systems include:

  • Hot Water Tank - This is the most common appliance for heating hot water. Electricity or natural gas is used by the tank to create hot water which is stored ready for use. The advantage of this system is rapid access to ready hot water, the disadvantage is a limited immediate supply and energy losses from holding hot water when not needed.
  • Combination Systems - For homes with hot water heating, it is possible to exchange some heat between the heating system boiler and the domestic hot water. The advantage is in less water heating equipment in the home but the disadvantage can be using a high-energy heating appliance through the non-heating system to heat domestic hot water only.
  • On-Demand Hot Water - On-demand systems do not keep a reserve of water heated and instead use high-energy heaters to heat water when hot water flow is requested. These systems can be central (i.e. one for the whole home) or localized (i.e. one for each hot water tap). The advantages are virtually unlimited hot water once running and energy savings when not in use. The disadvantages can be delays in getting hot water from initial start up and high initial costs of installation.
  • Commercial Systems - Condo's may have in-suite water heating equipment in the forms above but it is very common for the building to share one or more commercial boilers and storage tanks for domestic hot water. This system can be more efficient for the building as a whole as stored hot water will be cycled more often by users increasing efficiency. These systems are much more expensive than residential units but the costs are shared by all strata owners.


Drains and Venting

Showers, toilets, dishwashing, and hand washing all run the supply water nearly immediately down the drain.  Our homes therefor need to have a piping system to drain the 'waste' water safely away from the home. Unlike supply piping which is constantly under pressure from the utility water supply, drains only use gravity and waste water flow from the home to move water through the pipes.


Waste water pipes, like supply pipes, have seen many generations of materials used in the last century:

  • Legacy Materials - Lead, iron, clay, and galvanized piping have all been used in the past for drains. As drains use gravity rather than pressure to flow, the risks of deterioration are lower so these drain materials may still be in use even through original water supply pipes had been replaced. While these drains may continue to operate for many more years, home inspectors should identify these materials as being at the end of the expected service life.
  • Copper and Steel - Copper and steel pipes were more common in residential construction in the mid-1900's and continue to be common in larger commercial applications like some condos, particularly within fire stops as they won't burn like plastic piping will. There is no reason for home inspectors to be concerned about these materials unless they are failing to perform correctly.
  • Plastics - ABS and PVC piping have become the most common piping in homes today. In Canada, PVC is required by most code authorities while in the USA, ABS is the more common material. These plastic waste water materials, when correctly installed, have a history of excellent performance.


As there is no water pressure pushing the waste water in the drain pipes, any blockages or negative pressure in the pipe will stop the flow of water. In order to prevent negative pressures, drain pipes are 'vented' which allows the pipe to breath as water flows past. As we don't want these air vents to exhaust fumes or back up liquids into our homes, they are run all the way up and out of the roof and are visible as small pipes standing about 1' above the roof surface. Vents can be no further than about 10' from the fixture drains which is why many vent stacks are needed in large houses. Kitchen island sinks prevent a very big challenge for proper venting and in these cases a mechanical device called an auto-vent may be used under some code authorities.


Blockages in drain pipes from stuck waste materials are a common maintenance item. Accesses are typically available in the bottom of p-traps and at various access points along the drain piping in the home including the main drain stack. The drain accesses usually are set in the side of the piping and have a cap on them with a square knob for the plumber to attach a wrench. For toilets, a plunger is the most common tool for clearing blockages.


This incorrect 'S' trap will siphon water out of the air seal allowing sewer gasses to enter home.

Drain piping and vents have a major life safety consideration which is dangerous sewer gasses. Organic material in waste water from toilets and food debris decomposes in the sewer system and creates life threatening and explosive gasses like methane. In order to prevent these gases from backing up through the drains into the home, each drain requires a 'P' trap to capture a small amount of waste water which creates a water seal in the pipe preventing gasses from entering. Toilets integrate a 'p' trap in the design of the toilet itself. A common deficiency found in home inspections with amateur plumbing is missing or incorrect P traps. One common incorrect trap configuration is the 'S' trap which actually siphons the trap water out removing the air seal. The life safety concern around sewer gases is another reason only licensed Plumbers should make any changes to a home plumbing system.


Leaks from drain lines have different concerns than from supply lines. Supply lines are constantly under pressure which means a leak will continue until it is fixed sometimes resulting in major home flooding. A drain leak is not under pressure and will only leak as water passes by. Drain leaks can go unnoticed for long periods or time, particularly in unfinished crawlspaces or basements. Leaks in finished spaces will often show up initially as stains on ceilings. The other concern for drain leaks is that it may involve waste water which can carry dangerous bacteria. Repairs are often easy to do however it may require opening up sections of walls or ceilings to access the plumbing.


Sewer, Waste Water, and Storm Water

The water system in our homes is a cycle with water entering on the supply side and leaving on the sewer side. The final pluming connections on our home are where the waste water enters the municipal sewer system. Many municipalities have two sewer systems. One for domestic waste water which goes to a sewage treatment plant, and another which connects to the 'storm' water which may flow directly to streams and rivers. This can mean two connections to the sewer systems from many homes, particularly those with underground downspout connections from roof gutters which send water to the storm water system. 


The main drain stack (stack is a term for a vertical drain pipe) in the home turns towards the street at the lowest level of the home plumbing and is directly connected with the city sewer. One risk of sewer systems, particularly in low lying areas, is sewer backups. In flooding conditions, the municipal sewer system may no longer be able to drain away and water will back-up from higher up the system and flow backwards into lower homes. A back-flow preventer can be installed to ensure water only travels one way out of the home to prevent sewer back ups.


Homes in rural areas may not have access to municipal sewer systems. Septic tanks and septic fields are two common systems for removing waste from rural homes. Where it is not possible to discharge waste into the ground soil with a septic field or drain, it may be necessary to have the waste pumped away by trucks on a regular basis. Because of the complexities and health issues with managing waste water, home inspectors should leave septic field investigations to the experts.


Other Plumbing Systems

There are additional pluming systems that may be in place in homes:

  • Fire Sprinkler Systems - These systems fall under strict fire codes and require inspections by specially licensed fire safety professionals and are not reviewed in home inspections.
  • Sump Pumps/Sewage Ejectors - There are times when the local sewer system connections are higher than the lowest drains in the home. In these cases, water needs to be collected in a sump which is then mechanically raised higher for sewage draining with a pump. Home Inspectors will review these systems to ensure they appear to be functioning correctly.
  • Hot Water for Heating - Hot water heating systems are covered by home inspectors in the heating portion of the inspection
  • Whole Home Water Filtration - In order to improve water taste, some home owners put in whole home filters. These are considered an accessory to the home and are not investigated in a home inspection.
  • Lawn and Garden Sprinklers - Visible connections to these systems inside the home are inspected for any leaks but the lawn components and proprietary electronic and timers are not included in a home inspection and require an expert in this industry for evaluation.


Final Thoughts

Home plumbing systems use very simple principles like gravity, pressure, and pipes to deliver running hot and cold water where we want in our homes and as long as they operate properly, there is very little thought or maintenance given to the system. However, when things go wrong in plumbing systems, damages can often be very expensive to repair. To prevent damage or life safety concerns, always have a licensed Plumber perform work on home pluming system. Lastly,  before you buy a home, have a professional home inspector review the materials and function of your plumbing system so you know your home will be safe and solid.


By James Bell - Owner/Operator of Solid State Inspections Inc.