TDS — Total Dissolved Solids

High vs. low TDS on plumbing

Total Dissolved Solids (TDS) is a measure of everything dissolved in your water, including minerals, salts, and metals. Because water is the "universal solvent," its behavior inside your plumbing is entirely dictated by how "full" it is of these dissolved solids.

Water at 25 ppm and water at 500 ppm represent two extreme ends of the water chemistry spectrum, and they destroy plumbing in completely opposite ways.

Low TDS water (25 ppm)

Water with a TDS of 25 ppm is incredibly pure (similar to reverse osmosis or distilled water) and has almost zero mineral content. This extremely pure water "seeks" chemical equilibrium by dissolving materials it encounters. When these are metal pipes…

• Corrosion and leaching: Low TDS water acts as a weak acid as it flows through plumbing, stripping copper, lead, zinc, and iron directly from the walls of the pipes to satisfy its need for ions.
• Pinhole leaks: Over time, this constant leaching thins the metal, eventually resulting in microscopic pinhole leaks, particularly in copper piping and at pipe joints.
• Fixture staining: You will often see the evidence of this pipe decay in your sinks and tubs. Copper pipes leave striking blue-green stains on white porcelain. Galvanized steel pipes will leave orange rust stains.
• Appliance impact: It will rapidly eat away at the sacrificial anode rod in a standard water heater, leading to premature rusting of the water heater tank itself.

High TDS water (500 ppm)

Water with a TDS of 500 ppm is quite high in dissolved solids, which almost always include high levels of calcium and magnesium (the minerals that cause water hardness). Rather than taking material away, this water drops material off.

• Scaling and clogging: Because the water is at its maximum carrying capacity, any change in temperature or pressure causes the dissolved minerals to precipitate (fall out of solution). These minerals bind to the inside of the pipes, creating a rock-hard crust known as scale.
• Reduced water pressure: Over months and years, this scale builds layer upon layer, slowly shrinking the inner diameter of the pipes. This severely restricts water flow and lowers the water pressure throughout the house.
• Appliance destruction: When this water is heated, scaling accelerates dramatically. Your water heater elements become completely encased in a thick rock shell, causing them to overheat, consume massive amounts of electricity, and eventually burn out. It also clogs the tiny internal valves in dishwashers, washing machines, and coffee makers.
• Fixture crust: Faucets, showerheads, and drains will develop a stubborn, hard white crust that is difficult to remove without harsh chemical acids.
• Corrosion cells: Non-uniform scaling leads to the formation of corrosion cells.