Does Reverse Osmosis Remove Arsenic?

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Arsenic might sound like something that doesn’t concern you – it was just used as a poison around 500 years ago, right?

Actually, arsenic is still around today. It’s a natural component that can get into ground water from rocks and soil.

According to data from the WHO, at least 140 million people in countries around the world have unknowingly been drinking arsenic from ground water contamination at levels higher than the maximum recommended for public health (10 ppm).

Considering at best, arsenic causes stomach cramps, vomiting and confusion, and at worst, it can kill us, it’s no surprise if you don’t want to chance drinking it in your water.

In this guide, I’ll be sharing one of the most effective methods of removing arsenic from drinking water: reverse osmosis (RO for short). I’ll walk you through the reverse osmosis process, shine a light on some of the less appealing aspects of RO treatment systems, and highlight some of the considerations you should make when purchasing an RO unit.

🚰 How Does a Reverse Osmosis System Remove Arsenic?

Reverse osmosis (RO) filtration systems use a near-failsafe method to remove hundreds of contaminants, including arsenic, from water.

Water is forced through a pre-filter, carbon filter, post-filter, and a reverse osmosis membrane, at a high pressure. The carbon filter in an RO system can remove between 40% and 70% of water arsenic, but it’s the semi-permeable membrane that’s best at removing this contaminant.

The membrane consists of thousands of tiny pores of around 0.0001 microns – these are too tiny for arsenic, which is around 0.1 microns, to pass through. Arsenic and other contaminants rebound against the membrane, and are flushed down a drain during the filtration process.

Membrane Filtration Process

📊 How Much Arsenic in Drinking Water Does RO Remove?

Arsenic in drinking water poses a serious risk to public health, so you’ll be happy to know that RO is highly capable when it comes to drinking water arsenic removal.

Though the effectiveness of the system depends on its unique design, most reverse osmosis systems are able to remove arsenic at around 80% to 99% effectiveness. This makes RO one of the best water treatment options for arsenic removal.

🧫 What Other Contaminants Do RO Filters Remove?

It’s highly likely that your drinking water supply contains more than just arsenic. RO greatly improves your water quality by removing up to 99.9% of all total dissolved solids (TDS).

The thorough filtration process can greatly reduce most contaminants from your water, including chemicals, metal ions, pathogens and pharmaceuticals. Common contaminants like chlorine, lead, radium, copper, magnesium, calcium and salts can all be removed using a reverse osmosis system.

There are a few contaminants that this type of water treatment may not be quite as effective at removing from water, including bacteria, viruses, dissolved hydrogen sulfide, some solvents, pesticides, and VOCs.

👎 Downfalls of Point of Use RO Systems

Though it’s considered one of the best at-home drinking water treatment solutions of all time, reverse osmosis still has its downfalls:

Takes Out Healthy Stuff Too

Reverse osmosis filtration is so effective that it doesn’t just remove arsenic and the other bad stuff – it also removes the minerals that are good for our health, like calcium and magnesium.

While we can still get these health-enhancing minerals from elsewhere in our diets, you might prefer for your drinking water to contribute to your magnesium and calcium RDI. In that case, you’ll need to purchase a remineralization filter or mineral drops to enhance your water after RO filtration.

Can Be Expensive

There are plenty of options when it comes to cost, but generally, reverse osmosis treatment can be pretty expensive. You pay a premium for the highest quality system that’ll give you the best long-term arsenic-removal results.

In fact, if you find a reverse osmosis unit that’s suspiciously affordable (anything less than $150 for the whole thing), you should probably investigate the manufacturer before you part with your cash.

You’ll need a budget of at least $300 for a top-of-the-range RO unit.

Creates Wastewater

The RO membrane isn’t like a water filter – it won’t cling onto contaminants and collect them in its media. Instead, contaminants rebound against the membrane, and they need to be flushed from the system to prevent them from building up in the RO chamber.

When contaminants are flushed away, they take a bit of water with them. The amount of wastewater a reverse osmosis system produces will determine its efficiency – but RO treatment on a whole naturally wastes water as part of the process, making it a less efficient filtration method than others.

Requires Maintenance

Reverse osmosis systems usually last for more than 10 years. Within this time, you’ll need to carry out regular maintenance to keep your system working at its best.

The system’s filters will require changing (after every 6-9 months or 12 months, depending on the system). You’ll also need to replace the membrane at least every 2 years, and follow any specific cleaning instructions in your user manual. If you forget to change your membrane, you’re at risk of contaminants, including arsenic, being able to get through the system.

Reverse osmosis requires more maintenance than, say, buying bottled water, but the perks of getting your own filtered water from home make the small amount of work worth it.

💭 Considerations When Looking for an RO System

Before rushing into a RO filtration purchase, consider the following things:

Your Water Quality & Chemistry

The quality and chemistry of your drinking water may affect the way that your RO unit works.

Water that’s on the more acidic side may damage the RO membrane, as will water with a high hardness.

In any case, the more contaminated your water is, the quicker you’ll clog your RO filters and wear out the membrane. This will affect the frequency of maintenance you’ll need to carry out.

While you might only want to remove arsenic from your water, reverse osmosis systems are designed to greatly reduce nearly every common contaminant. So if your drinking water quality is actually relatively good, aside from arsenic, you might want to consider whether RO treatment is worth paying for.

Efficiency Ratio

All reverse osmosis units are given an efficiency ratio that indicates how much water is wasted per gallon of clean, pure water produced.

Traditionally, RO units had to waste up to 4 gallons of water to produce a single gallon of pure drinking water. This figure isn’t great; you’d likely notice that your water bill was a little higher than usual if you were wasting 4 times more water than you were producing with your RO unit.

Luckily, many point-of-use RO treatment solutions are far more efficient nowadays. Some units have a much better ratio of 2:1, while some even have a ratio of 1:1 – meaning only one gallon of water is wasted for every one gallon produced. Considering the nature of the RO process is to waste water, this is about as good as it’ll probably ever get.

Type of System

There are several types of point-of-use and point-of-entry RO units available to choose from today. The system you opt for will largely depend on your budget and your requirements.

For instance, if you have a bigger budget and you want to deliver pure, arsenic-free water all around your home, a whole-home RO system is a great option. However, these systems certainly aren’t necessary if you’re just looking for drinking water arsenic removal.

There are two popular point-of-use RO units: under-sink systems and countertop systems. These treat tap water at a specific point in your home (under your kitchen sink or on your kitchen countertop, normally).

Point-of-use systems are smaller, more compact and more affordable than whole-home treatment options.

Your Budget Available

Your budget will play a big part in the RO treatment solution you go for.

No matter what, an RO unit will likely set you back at least $300 and can certainly go higher based on technology and efficiency.

RO water filters that use the most modern or convenient technology, such as tankless systems and systems that have a 1:1 wastewater to pure water ratio, will usually be priced a little higher for their benefits. Additionally, as I mentioned above, you’ll generally pay much more for a whole-home, point-of-entry filter than a point-of-use system.

There are plenty of great deals to be had, so when you’re shopping around for reverse osmosis systems, look out for discount codes and offers from water filtration experts like myself. Just be wary of paying a particularly low price for a reverse osmosis system, as price is generally a reflection of quality.

🔠 Additional Options For Removing Arsenic

Aside from RO filters, there are several other filter systems that can remove arsenic from tap water. A distillation unit can remove 90-100% arsenic, making it just as capable as reverse osmosis. Ion exchange systems are also highly capable of arsenic reduction. Additionally, an activated carbon unit can offer up to 70% arsenic reduction, as well as removing the likes of chlorine and lead.

Some of these systems cost less than reverse osmosis systems, so they’re worth considering if your budget is small, or you’re new to water filtration and don’t want to splash out lots of money on a treatment option just yet.

Whatever your decision, make sure you do your research. I have plenty of handy reviews and in-depth guides to check out if you’re still considering your options.

  • Jennifer Byrd
    Water Treatment Specialist

    For 20+ years, Jennifer has championed clean water. From navigating operations to leading sales, she's tackled diverse industry challenges. Now, at Redbird Water, she crafts personalized solutions for homes, businesses, and factories. A past Chamber President and industry advocate, Jennifer leverages her expertise in cutting-edge filtration and custom design to transform water concerns into crystal-clear solutions.

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