We recently received an email inquiry from Lisa containing a question about water treatment systems for people with compromised immune systems.

My son has just been diagnosed with an immune deficiency, and I should be sterilizing his drinking water -which I am doing by boiling for him. I am wondering if distilled or reverse osmosis, bottled water would effectively remove bacteria from the water, and be a safe alternative. Would one be better then the other.

Thank you for your time,


Thank you, Lisa, for your question and it pains us to learn of your son’s condition. We hope that modern medicine can find a way to help your son live a long and healthy life.

Regarding your question about the best way to sterilize water for people with compromised immune systems, the EPA and CDC co-released a document back in 1995 that gives a lot of useful information on the topic entitled Guidance for People with Severely Weakened Immune Systems.

Below you will find excerpts from that document relating directly to the questions you asked:

  • Cryptosporidium has caused several large waterborne disease outbreaks of gastrointestinal illness, with symptoms that include diarrhea, nausea, and/or stomach cramps. People with severely weakened immune systems (that is, severely immunocompromised) are likely to have more severe and more persistent symptoms than healthy individuals. Moreover, Cryptosporidium has been a contributing cause of death in some immunocompromised people.
  • Although data are not sufficient for EPA/CDC to recommend that all severely immunocompromised persons take extra caution with regards to their drinking water, individuals who wish to take extra measures to avoid waterborne Cryptosporidiosis can bring their drinking water to a full boil for one minute. Boiling water is the most effective way of killing Cryptosporidium.
  • Only point-of-use filters that remove particles one micrometer or less in diameter should be considered. Filters in this category that provide the greatest assurance of Cryptosporidium removal include those that use reverse osmosis, those labeled as “Absolute” one micrometer filters, or those labeled as certified by NSF International under standard 53 for “Cyst Removal.” …. Water treated with a point-of-use filter that meets the above criteria may not necessarily be free of organisms smaller than Cryptosporidium that could pose a health hazard for severely immunocompromised individuals.
  • Many, but not all, brands of bottled water may provide a reasonable alternative to boiling tap water. …. Any bottled water treated by distillation or reverse osmosis before bottling assures Cryptosporidium removal.

  • Neither EPA nor CDC maintains a list of point-of-use filters or bottled water brands that meet the above criteria. NSF International can provide a list of filters that meet the NSF criteria.

We suggest you take a look at the NSF Web Site to see what systems meet their requirements. In a situation like yours, you will want to make certain the product you purchase will accomplish all your objectives — and then some.

Pentek RO-3500 Reverse Osmosis System

One system we came across recently, the Pentek RO-3500 Monitored Reverse Osmosis System,

NSF Tested & Certified Standard 58 for reduction of TDS, Fluoride, Turbidity, Lead, Nitrates, Selenium, Arsenic, Copper, Cadmium, Barium, Cyst, and Radium.

The Pentek R0-3500 features the 3 stage system, one ROM-230TN membrane, a D15 sediment filter, a D20 carbon filter, and one long-reach lead-free faucet. Unit comes with a standard installation kit and instructions.

Another feature of the the Pentek RO3500 which makes it quite nice… an electronic monitoring system that keeps track of the water filters cartridges’ lifespans and informs the owner when they need replacing.

What elements does the RO-3500 Reverse Osmosis System reduce and/or eliminate? The unit has the ability to filter out the following elements as well as many other chemical compounds:

For more information on the Pentek Reverse Osmosis System mentioned above, please read its detailed specifications on FiltersFast.Com.

One final word

Use of a reverse osmosis systems does NOT guarantee the elimination of ALL possible biological contaminants since some biological contaminants have sizes smaller than the membranes in RO units can filter out.

For that reason you may want to consider adding a UV Sterilizer to your filtration setup. These devices render biological contaminants incapable of reproducing by altering their genetic structure with specific wavelengths of light.