Does an R.O. Remove Parasites Such As Bacteria, Cysts Or Cryptosporidium?

Written By Kasidy Kersey

When Houston homeowners hear about parasites like bacteria, Giardia, or Cryptosporidium in water, one of the first questions they ask is: “Will my reverse osmosis system protect me?”

The short answer:
Reverse osmosis is extremely effective for removing cysts and many microorganisms, but it may need help for full protection against all bacteria and viruses.

Here’s the clear breakdown of what R.O. can do, what it can’t do alone, and the best setup for total safety.

What Reverse Osmosis Does Remove

The R.O. membrane has extremely small pores — about 0.0001 microns — which is far smaller than most waterborne parasites.

R.O. Removes Very Effectively:

  • Giardia cysts

  • Cryptosporidium

  • Protozoa

  • Parasitic cysts and oocysts

  • Most waterborne microorganisms too large to pass through the membrane

Because cysts are large (2–15 microns), they are effortlessly rejected by the R.O. membrane.

For homeowners on city water, this filtration level is more than enough for drinking water safety.

What Reverse Osmosis May Not Remove on Its Own

Where things get more complicated is with bacteria and viruses.

Some types of bacteria are small enough to slip through tiny imperfections in the membrane or can grow inside an improperly maintained system.

R.O. Alone May Not Remove:

  • All bacteria

  • All viruses

  • Any contamination occurring after filtration

Reverse osmosis is not classified as a certified microbiological purifier on its own.

This is especially important for:

  • Homes on well water

  • Homes with known bacterial contamination

  • Homes with older plumbing

  • Homes with stagnant water or pressure tank issues

The Best System for Parasite and Bacteria Removal

For homeowners needing full microbiological protection — including those on well water — the most effective solution is:

1. Reverse Osmosis + Carbon Filtration

Removes chlorine, chemicals, cysts, metals, and dissolved solids.

This is what our home uses!

2. UV Disinfection (Ultraviolet Light)

Installed after the R.O. system, UV neutralizes:

  • Bacteria

  • Viruses

  • E. coli

  • Coliform

  • Salmonella

  • Hepatitis A

  • Microorganisms that R.O. cannot handle alone

UV is chemical-free, safe, and extremely effective.

3. Optional: Whole-Home Pre-Filtration

If well water carries sediment, iron, sulfur, or cloudiness, you need pre-treatment to protect both the R.O. and the UV system.

This layered approach ensures true, comprehensive protection.

Why This Matters for Houston Homes

Houston municipal water is disinfected and generally free from parasites.
However:

  • Private wells may develop bacterial contamination

  • Aging infrastructure can introduce microorganisms

  • Homes with storage tanks or long plumbing runs may see bacterial regrowth

If you’re unsure whether your water is at risk, a test gives immediate clarity.

Why Environmental ProTech

At Environmental ProTech, we design water purification systems for Houston-specific conditions, whether you’re on city water or a private well.

When you schedule a test, we will:

  • Test for bacteria (coliform and E. coli, if needed)

  • Check turbidity, sediment, chlorine, and other factors affecting microbiological risk

  • Recommend whether R.O. alone is sufficient or if UV should be added

  • Build a custom system designed for your family’s safety

We don’t guess — we test, design, and protect.

Call now to schedule your free water test and learn whether your home needs R.O. alone or R.O. with UV for complete pathogen removal.

Call to schedule your water test

PS. We have over 30 years experience in bringing clean water to the Houston Homeowners. Our reviews speak for themselves! If you want clean drinking water from your faucet, contact us at 281-495-4420 to schedule your free water test today.

Sources & Further Reading

Kasidy Kersey
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