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Supply Pipe in Pre-1940 Homes

Build era is the best single predictor of what your supply pipe is made of, and the material is what decides whether the pipe itself can be the cause.

Old metal supply pipes running across a basement ceiling

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Housing from this period generally means galvanized steel supply pipe throughout, most of it decades past the point where the zinc lining has gone and rust has begun closing the bore from the inside. In houses this old the pressure loss is usually gradual rather than sudden, and it affects the whole house rather than one tap.

What that means in practice

Two questions follow from the material. First, can the pipe itself narrow? Galvanized steel can and does; copper, PEX and polybutylene do not. Second, if the pipe is not the constriction, what is? In practice it is a valve, the supply into the property, or the municipal side.

A gauge reading settles which. Below 40 psi static is genuinely low; 45–80 psi is the normal band. Normal and low ranges as published by Grundfos in its homeowner guide to low water pressure.

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Other eras

Build era is a strong predictor, not a guarantee. Plenty of houses have had part of the supply replaced and part left alone, which is exactly why a pressure reading beats an assumption.