Reverse osmosis drinking water, explained
RO drops TDS way down by forcing water through a membrane, but it needs pre-filtration to survive Phoenix's chloramine and hardness, and many systems add minerals back afterward so the water doesn't taste flat. Filters and membranes are wear items — change them on a schedule, not when taste tips you off.
Reverse osmosis (RO) systems are one of the most common ways homes and businesses get better-tasting drinking water at the tap. Here's what's actually happening inside one, and what owning one involves.
Why pre-filtration matters here
An RO membrane is the last stage, not the first. Ahead of it, a good system runs sediment and carbon pre-filters that strip out grit, chlorine and chloramine before the water reaches the membrane. Skip that step in Phoenix water and the membrane takes the abuse instead — chloramine degrades some membrane materials over time, and hardness minerals scale the membrane surface, cutting its life down from years to months.
TDS in vs. TDS out
Total dissolved solids (TDS) is the standard way to measure how much is filtered out. Phoenix tap water often runs 400–800+ ppm TDS depending on source; a properly working RO system typically drops that to a small fraction of the feed number at the faucet. Checking TDS in and TDS out with a simple meter is the fastest way to tell if a membrane is still doing its job — a rising "TDS out" reading over time is usually the first sign a membrane needs replacing.
Remineralization — and why coffee shops care
Stripping out that much TDS also removes minerals that give water body and flavor. Water that's too pure can taste flat, and it can actually be more chemically aggressive toward metal fittings and equipment because it's "hungry" for minerals to pick back up. Many RO systems add a remineralization stage after the membrane for exactly this reason. It matters even more for espresso and specialty drink equipment — brewing with water that's stripped too clean produces flat-tasting shots and can be harder on boilers, which is why commercial RO setups are specced differently than a basic under-sink unit.
What it doesn't do
A typical RO system treats water at one point — a faucet or a machine's line — not the whole building. It won't stop scale buildup in a water heater or shower. It also produces some wastewater as part of the filtration process, which is a normal part of how the membrane works, not a sign of a problem.
Upkeep: how often things change
Sediment and carbon pre-filters are the parts that wear fastest and typically get swapped most often; the membrane itself lasts longer but isn't permanent, and post-filters or remineralization cartridges have their own schedule. Skipping changes doesn't just hurt taste — it shortens the life of every stage downstream of the clogged one. This is the kind of maintenance we handle as part of repair & rebed service.
Getting started
If you already have an RO system and it needs a filter change or isn't performing like it used to, see our services page. If you're deciding whether RO is worth adding, just send us your info and we will point you the right way.