Reverse Osmosis Systems: The Twin Cities Guide

Reverse osmosis is the most thorough residential water purification technology available. A properly certified RO system removes 95 to 99 percent of dissolved solids, including lead, fluoride, arsenic, nitrates, and per NSF/ANSI 58 certification, PFOA and PFOS. In the Twin Cities, RO is especially valuable in the East Metro PFAS contamination zone and for any household concerned about specific dissolved contaminants. Most homes get an under-sink RO at the kitchen tap. PFAS-zone homes typically need whole-home certified filtration.

How reverse osmosis works

A reverse osmosis system forces water through a semi-permeable membrane that allows water molecules through but blocks dissolved solids, metals, and most other contaminants. The contaminants flush to a drain. The purified water flows to a storage tank or directly to a faucet.

A typical residential RO system has 4 to 5 stages:

1. Sediment pre-filter to catch particles
2. Carbon pre-filter to remove chlorine (which would damage the RO membrane)
3. RO membrane for the actual purification
4. Carbon post-filter for taste polishing
5. Optional remineralization stage to add back calcium and magnesium for taste

What RO removes

Per NSF/ANSI Standard 58 certification, properly certified RO systems are tested and verified to reduce:

• Lead (relevant for older Twin Cities homes with pre-1986 plumbing or service lines)
• Arsenic (relevant for some private well users)
• Nitrates (relevant for private wells in agricultural areas)
• Fluoride
• PFOA and PFOS (relevant for the East Metro PFAS zone)
• Cadmium, chromium, copper, selenium, total dissolved solids
• Chlorine and chlorination byproducts

What RO does not do

• It does not soften water (does not remove calcium and magnesium for the rest of the home; only at the RO output tap)
• It does not remove gases (hydrogen sulfide sulfur odor needs separate treatment)
• It does not treat bacteria reliably (UV or chlorination needed for well water with bacterial concerns)
• It does not improve water pressure (in fact, RO output is lower flow than the main supply)

Under-sink vs whole-home

Under-sink RO is installed at the kitchen sink and provides purified water at a dedicated faucet (and optionally to the refrigerator ice maker). Standard for drinking and cooking water. Lower cost. Typical installed price: $800 to $1,500 in the Twin Cities.

Whole-home RO is much rarer and more expensive. Required when the homeowner wants RO-purified water at every fixture in the home. Standard recommendation in the East Metro PFAS zone where bathing exposure is a documented concern. Typical installed price: $3,500 to $7,500 in the Twin Cities depending on home size and configuration.

For the East Metro PFAS contamination zone, a more common configuration is whole-home certified PFAS filtration (NSF/ANSI 53) plus under-sink RO at the kitchen for additional polishing. This addresses bathing exposure across the home and final-mile purification at the drinking tap.

When RO is the right answer in the Twin Cities

• You live in the East Metro PFAS zone and want a verified barrier at the drinking tap
• Your home has lead service line or pre-1986 plumbing concerns
• You have a private well with documented nitrate, arsenic, or specific contaminant concerns
• Bottled water purchase exceeds $200 per year (RO pays back fast)
• You have specific taste or odor concerns that carbon filtration alone has not resolved

What to look for in an RO system

1. NSF/ANSI 58 certification for the specific contaminants you care about. Read the certification language. Generic “purifies water” claims are not certifications.
2. Replaceable filter cartridges with reasonable cost (avoid proprietary high-margin cartridge brands)
3. Stainless steel or BPA-free plastic tank rather than older galvanized tanks
4. TDS meter to verify output purity over time
5. Drain saddle or air gap properly installed
6. Designated faucet at the kitchen sink, ideally lead-free brass or stainless

The Twin Cities setup we recommend most

For most non-PFAS-zone Twin Cities homes:

1. Properly sized whole-home water softener (Fleck or Clack metered valve)
2. Under-sink RO with NSF/ANSI 58 certification at the kitchen tap
3. Sediment pre-filter if on well water

For East Metro PFAS-zone homes:

1. Whole-home NSF/ANSI 53 certified PFAS filtration before the softener
2. Properly sized whole-home water softener
3. Under-sink RO at the kitchen tap for final polishing

Free in-home water test from A.J. Alberts confirms what your specific water needs.

Call 651-738-0580 or schedule a free water test. See our reverse osmosis page.