Most of the sections in this home maintenance series are relatively short, I guess I kinda like to get straight to the point. Today I would like to describe items inspected during the plumbing portion of the inspection.
Main Supply
I usually start at the main water meter and shutoff or the pressure tank an main line if on a well system. A typical home inspection does not include wells, but we do pick up the system where the main line enters the foundation as we do on a home located in the city. I like to first check the floor and the general condition of the supply line directly 
after the meter. If the piping is copper is there a green like substance present? This is caused by leakage or condensation forming on the lines. It is best practice to insulate the supply line for about the first 6 feet after the meter or pressure tank. This will reduce or eliminate the formation of condensation. I will also check the main valve at this time. Can it be completely turned off without obstruction? Is it readily available in the event of emergency? Just last week I was at a home in Brodhead that the previous owner installed the water softener loop near the meter and the main shutoff could only be partially turned off. This could have caused flooding if a leak were to occur.
Supply lines, Fittings, and Transitions
After we examine the main, I then follow all of the visible supply lines in the lower level, generally the basement in our area, but occasionally this required crawling the crawlspace areas. I pay especial attention to fittings, valves, and soldered joints. It is not 
uncommon to fins calcium buildup in these areas, this indicates past leakage. As these minerals buildup at the source of the leak, they generally seal the fitting. It is generally a wise idea to repair these areas. I also look for transitions from copper piping to galvanized piping. This is not allowed because a chemical reaction can happen and lead to galvanic corrosion. A dialectic union is required, Or a brass fitting can be used, under no circumstance can these two metals touch. One other common area for leakage is at the laundry supply valves. Gate valves always seem to show signs of corrosion or calcium from previous leakage. Monitoring these valves for leakage on a regular basis is always recommended.
Drainage
After the supply line inspection, I go back and examine the drain lines, I check each splice or transition just like the supply line inspection. Many times there are Splices from old cast piping to new PVC piping. These transitions should be scrutinized as they are a common place for leakage. Furnco fittings are a rubber transition that is secured with hose clamps. If not installed correctly, they can leak. Now, the most common area for leakage at drain lines is probably at the toilet flange. If it is possible to see from below check the sub-floor area around the toilet drain. Is there moisture staining? Does the toilet rock or move when pressure is applied? Replacement of the wax seal probably necessary if these conditions exist. I bought an investment property one time that had a small leak at the toilet. It had caused all of the studs to be rotten up to 8 inches above the floor, so this $3 part can be a big expense if not monitored.
One other drain issue I find on a regular basis is the use of “S” traps. This type of trap is not allowed as the movement of the water can create a suction and leave the trap dry. This may lead to the admittance of sewer gasses into the living area.
Vent
There isn’t much to maintaining the vent system, but one good item to check is that there IS at least one vent exiting the home. Surprisingly people remove all of the roof vents when they do a re-roof. This is a defective installation and should be repaired. I imagine their thought is to reduce the amount of roof penetrations, but surely there is another way. The venting system must “breathe” and allow for the admission or emission of air in order to protect the trap seal.
Water Heater
When inspecting the water heater the first item I am looking for is any corrosion on the tank. Often times supply line gate valve leakage can cause extensive damage at the top of the tank. Another common area for corrosion is at the base of the tank, especially 
when the tank is places directly on the concrete floor. A 2 inch are space is recommended beneath the tank to allow air to flow and keep the tank surface dry. In some jurisdictions insulation id required beneath the tank to reduce energy loss. 2 inches of polystyrene foam is usually utilized. Another important device is the temperature pressure relief valve (TPRV). This valve is designed to open when the pressure or temperature exceed a certain point. This prevents the tank from exploding. This valve must have a discharge pipe that extends to within 6 inches of the floor to prevent scalding of occupants that may be in the area. This is a very common defect because the discharge piping does not come with the water heater and if a homeowner does the install, they may not know of the requirement.
Summary
Mainly the plumbing portion of any home inspection is examining the fittings and transitions of the supply and waste piping. Generally signs of current and past leakage are easy to spot. It is advisable to do a plumbing inspection in your basement, crawlspace, and laundry areas on a regular basis to identify problem areas before a larger issue rears its ugly head.
-AZ
Aaron M. Zuehlke is the owner and inspector at Zuehlke Inspection Service, LLC, a full-service home inspection company serving Southern Wisconsin. Specializing in Home inspection, Radon Testing, Mold Testing/inspection and Residential Thermal Imaging. He can be reached by email at Aaron@Zuehlkeinspections.com or by calling the office at 608-931-7485.