Dead end in pipes and legionella risk

Question

Today a plumber removed a sink from my house and sealed the two corresponding pipes at the location where they branch from the rest of the system. I expressly asked him to do this because I wanted to avoid having a dead run of pipe in my walls where bacteria could develop and cause serious health risks.

This is the end result. I marked in red where the dead leg starts for each of the pipes that got cut.

I've been reading online about the risk of bacteria such as legionella developing in the system and the recommendation seems to be that the dead leg's maximum length should be at most 1.5 times the diameter of the pipe itself. The dead legs shown in the picture are about 4 times the diameter.

I would like to understand whether this poses a health risk and whether I ought to ask the plumber to come and shorten the pipes.

Answer 1

I would not be overly concerned about this unless it was the highest point in your plumbing or if you had low water pressure from the water supply (or if you are on well water).

These couple of inches extra should be flushed with water at all times and recycled with the rest of the water supply. There is no reason to believe that the water in these small sections would remain stagnant, as they are just way too small to have "standing" water.

If you are concerned I would have the plumber not cap these at all, take out the nearest T and change it for a right angle.

Now there are a TON of benefits to block framing (from the materials I am guessing France or Italy) but plumbing and rerouting the plumbing... no. We simply don't have many instances in the US like this because the plumbing is easily modified inside 2x construction.