Does Reverse Osmosis Filtered Water Require Remineralization?

My grandma used to say I should not drink distilled water. I want to understand if that's true / applies to RO water and if RO-filtered water needs remineralization.

This is a blog where I go in-depth into questions and topics, I am personally interested in related to contamination and toxicity. The goal is to break down and interpret the actual data behind many of these compounds in the news for a non-chemist like me. Each blog is based on secondary research, primarily from published articles found through Google Scholar and known academic journals, and experience formed during my work with chemical analysis.

TLDR

• World Health Organization (WHO) state that drinking pure (distilled, reverse osmosis-filtered) water is not healthy.

• Such filtered water should be remineralized. Research goes beyond the usual suspects of calcium and magnesium as ideally water would contain many more beneficial trace minerals.

• One should still weigh up the risks in cases where water alternatives, such as local wells, are contaminated.

Thanks ChatGPT

Reverse Osmosis Filtration Recap

You might have read my previous post (Can We Filter PFAS Forever Chemicals from Water?) going into details on the available methods to filter for PFAS. The consensus and guidance is that Reverse Osmosis (RO) is the most effective filtration method for households as it comes to PFAS and also overall, even if it is quite energy intensive .

Reverse Osmosis uses fine plastic membranes (typically made of nylon/PA) to separate water and its contents under a high pressure environment. The method is highly efficient, cleaning most long chain PFAS and also the most efficient to filter for short-chain PFAS. It is so efficient in fact that apparently it filters most of the things in water, including toxic and active compounds (lead, nitrate, some bacteria, fluoride, chlorine) and also minerals which are healthy, such as calcium and magnesium (EWG, Research Paper).

There is also one footnote to RO filtration. During my research into nanoplastics (Nanoplastics In Water - Groundbreaking Findings on Quantities and Main Plastics) and the groundbreaking study on the topic released earlier this year, I concluded that RO nylon membranes could be a potential source of nanoplastics contamination in water due to the nylon membranes used. However, this today is only a theory and it is based on just one research publication.

Is Drinking Distilled and RO-Water OK?

There are a lot of claims online that it is perfectly fine to drink. But not that many credible sources which confirm so. I went looking for a source I could trust and two I have come up are from WHO and EWG, cited below. WHO are unambiguous around the risks, while EWG tone is more subtle in terms of risks.

WHO write (WHO Report, p.151) that drinking water which is free of anything is not good. Water purity is defined by the amount of total dissolved solids (TDS). Water with <100 mg/L of TDS starts posing health risks evidenced by both human and rat studies. These primarily relate to body giving up sodium, potassium, chloride, calcium and magnesium ions from the body to the distilled water as it passes through intestines. Apparently this is not fully mitigated even if food and diet contain sufficient quantities to compensate for it. In turn deficiencies in these minerals increase various health risks from tiredness to heart risks. Symptoms also do not have to be immediate and can take a long time to come in in full force.

The WHO study (WHO Report, p.153) then specifically cites RO-water as increasing the risk of calcium and magnesium deficiencies, which risk cardiovascular disorders, tiredness, weakness or muscular cramps. The effects are quickly manifested.

The report extends further citing lack of other nutrients as an additional risk of consuming highly purified water. Apparently the optimal content of minerals in water is:

• calcium levels of 40-80 mg/L,

• magnesium levels of 20-30 mg/L,

• bicarbonate ion content of 30 mg/L,

• TDS of 200-500 mg/L.

Low in minerals water is also more aggressive so an RO system early in the piping can end up introducing additional contaminants from pipes by the time it reaches a drinking glass (WHO Report, p.155, EWG).

There is also a taste issue. Purification increases water acidity and makes it flatter, meaning that the taste becomes less appealing

Bottom line is that highly purified water should ideally be remineralized afterwards.

Remineralization Goals

The general filtration standard of reference is the one by NSF (Website). NSF standards 60 and 61 cover the remineralization related to calcium and magnesium. However, this is with a focus of not introducing additional contaminants rather than monitoring if the healthy remineralization threshold is reached.

The following article (Article, 2010) provides good clarity on key mineral contents required and proposes a battery of minerals required for a fully sufficient remineralization (presented below). As we see this is a lot more extensive than just the calcium, magnesium and bicarbonate ion:

Source: Article

Remineralization Effectiveness of Available Systems

I could not find any information on this. Please let me know if you know anyone doing a good benchmark and testing routine on remineralization cartridges and approaches?

A few internet comments suggest that the impact is fairly minimal in adding back the minerals to sufficient quantities, while the PH increases.

Conclusion

RO water should best be drunk with remineralization performed. I suspect that the available remineralization cartridges fall far short of the recommended list of minerals to be added back.

However, one should also weigh up the alternatives. There are cases were a local well water can be rather dangerous, in which case RO water is probably a safer alternative. Ideally one should still remineralize it though.