You often see copper and galvanized steel plumbing mixed in residential water systems with nothing separating them other than a little thread sealant or Teflon plumbing tape. The galvanic connection (copper to steel) can be trouble-free for years or the steel plumbing can begin to corrode almost as soon as the connection is tight.

Back flow occurs in municipal water systems (or within a house) when there’s a sudden and severe drop in water pressure that causes water to flow back through pipes opposite the direction that it normally flows.

When a runaway car severs a fire hydrant, for example, parts of a municipal system will see a flow reversal as water gushes out the hole where the hydrant once stood. The same thing can happen if there’s a massive leak within your house.

Don’t forget, gas lines count as plumbing too. Connecting a new gas range or dryer to an existing gas line seems simple, but the job can quickly go awry when you try to hook up a flexible gas connector to the line and find that the connector doesn’t fit or you can’t make the connection gas-tight, no matter how tight you make the connection.

Pounding nails and driving screws is all well and good, until you puncture a copper or plastic supply or drain.

Plumbing is a tricky business, with rules that dictate how far you can place a fixture from the home’s drain-waste-vent line based on the pipe diameter and other arcane matters. The only way you can handle a big job yourself is to know the code and what it calls for in pipe sizing, fixture spacing and related matters.

You can’t make a neat water- or gas-tight joint unless the parts are neatly cut.

Only a soldered or glued joint doesn’t require sealant; everything else does.

If tight is good, really tight must be better. Right? Wrong.

It should be obvious: Make a thorough leak inspection before closing up and moving on.