Hard water carries dissolved calcium and magnesium. Those two minerals are the reason a kettle scales up, a shower head clogs, and soap refuses to foam.

A slab leak is a leak in a water line that runs under or through the concrete foundation slab your house sits on. In a slab-on-grade home, the supply pipes for both hot and cold water are often buried in or just beneath that concrete.

Hydrogen sulfide is the gas behind the rotten-egg odor, and your nose is remarkably good at catching it. People can detect it at concentrations well below one part per million, which is why a faint trace at the tap seems so strong.

Older homes were plumbed with air chambers to absorb this shock, short capped stubs of vertical pipe near fixtures that hold a cushion of trapped air. Air compresses; water does not. When that cushion is present, the shock wave pushes into the air pocket instead of the pipe.

Hard water is water carrying dissolved minerals, mainly calcium and magnesium. Those minerals are invisible in the glass, but when the water is heated or left to evaporate, they drop out of solution and cling to whatever surface is handy.

Most homes are comfortable and safe at 40-60 psi. Plumbing code draws a hard line at 80 psi: once static pressure exceeds that, a pressure-reducing valve is required because above it the risk of damage rises quickly.

Hard water is loaded with dissolved minerals, and those minerals come out of solution as scale wherever water is heated. Both heater types deal with that, but in different places.

Before anything else, check whether the discoloration appears in the hot water only or in both hot and cold. This single observation points you in the right direction.