Under an answer to How is the quality of tap water in Thailand? I commented:
Usually water in pipes is pressurized so that it comes out of the tap when you open it; is "dirty water making its way into cracks in the clean water pipes" really a known thing? Does it really happen, can you cite an authoritative source for this phenomenon? Sure during a major weather event water treatment plants can be overwhelmed, and breakage of pipes resulting in complete loss of pressure can allow inflow, but I don't think heavy rainfall itself can push dirty water into the pipes against normal levels of pressurization. I'm certainly happy to be proven wrong if you find something.
and someone replied
water coming out with pressure is due to gravity because the tank is on the roof. Usually tanks are filled with water from municipal sources and then that tank water flows through pipes into the building's houses.
to which I replied:
Sure that's quite common, but at what point is there negative pressure such that the dirty water can leak into the pipes? I know this is a DIY SE or Physics SE rather than a travel question, I'm just really curious if this is really a thing, or just something we imagine.
Now those pumps that "pull" water up to the tank on the roof are worrying me; can they in fact be so aggressive that they drop the pressure in a small diameter rural municipal water pipe so much that dirty water could leak in?
Are there other things that can happen, short of catastrophic pressure loss that can lead to this happening?