How Can Rainwater Be Purified? What’s The Easiest Way?

Rainwater dripping down from a gutter.

Collecting water from the sky is something that has been done since the dawn of time, it is the predominant source of water for a large amount of the world’s population even to this day. I grew up drinking nothing but rainwater, often collected straight off the roof of our house! Due to a variety of factors, however, this rainwater may need to be purified, the question is, how can it be purified and what is the easiest method?

Rainwater can be purified with a variety of methods from reverse osmosis to activated carbon and ultraviolet (UV) filters. A separate UV or carbon filter represents the easiest option to filter rainwater as they can be either retrofitted to existing taps or used as portable standalone devices.

If you are first wondering whether you should filter your rainwater, I encourage you to have a quick read of my article on the topic which explains general concerns and options.

Charcoal Filters: The Easiest

Activated charcoal filters vary in size and location, you may have previously noticed standalone filter jugs or in-situ filters attached to taps, chances are these are carbon filters. Activated carbon is extremely effective at removing a variety of contaminants from microplastics through to most microorganisms. Whether you need a retrofitted option to attach to your taps or a portable filter jug, both do a good job and are painfully easy, with near zero installation or inconvenience. Although Charcoal filters are very easy options to purify rainwater, if you are thinking about making a filter out of regular charcoal, it, unfortunately, won’t suffice, I wrote an article here explaining why. Does Regular Charcoal Filter Water? What’s The Difference?

The advantage of carbon filters is both their price and their ease of use, you can purchase a charcoal filter jug for less than $20 USD on Amazon that will work perfectly to improve rainwater quality. The example to the left is a Pur water jug that is slightly lesser known than brands like Brita however it actually has been proven to remove nearly twice the number of contaminants. Check it out on Amazon here.

Ever so slightly more expensive with around 30 seconds of installation time as opposed to zero, retrofitted charcoal filters are a great option for on-demand purified rainwater straight from the tap. The example on the right is under $30 USD and has the same great filtration mechanism as the jug above, the advantage of the jug is that you can keep it cool in the fridge, whereas this on-tap system has water on demand. Check out the on-demand system on Amazon here.

Ultraviolet: The Middle Ground

Ultraviolet water filters can be considered the middle ground, slightly more expensive than charcoal filters they also can generally help purify a lot more water than charcoal filters before they need any maintenance. I wrote an article explaining how long they’ll last and things you can do to prolong their life earlier. Ultraviolet filters are better than charcoal at removing microorganisms from water which is generally the primary concern with rainwater, however, they do not remove inorganic substances like microplastics or metals which charcoal is somewhat effective at. The options for ultraviolet filters range from extremely portable water bottles or pen-like devices to retrofitted on-tap solutions all the way to inline high-flow rate solutions for entire homes.

The SteriPen is certainly the most well-known of the portable UV treatment solutions and it works by simply inserting it into a water bottle or cup and turning it on for a minute. They are available for around $100 USD and they generally last for a long time, I have used them when hiking for years without issue and have seen them in the hands of experienced professionals the world over. You can check them out on Amazon here.

Much like the on-demand solution for charcoal filtration, the same is available for UV filters and they generally work pretty well. Near zero installation is required and they last for over a year, on tap solutions tend to work pretty well for most and the great thing is you can remove the filter and put it on a different tap in a matter of seconds if you have multiple sources you want to be purified. These are available for under 30$ USD on Amazon here. Personally, for on-demand solutions, I would opt for the charcoal option due to its ability to remove inorganic substances in addition to bacteria.

The most comprehensive UV system is also, unfortunately, the most difficult to install. In-line UV water treatment systems are a great option if you require large amounts of rainwater purified, for instance, if you rely on rainfall for all aspects of your life, rather than just drinking water. These would generally be installed in-line from the water source before it reaches the house plumbing. If you are quite handy, then installation shouldn’t be a problem and you can purchase suitable systems for around $200 USD on Amazon. however, I would recommend most people get the services of a professional when installing such a device.

Reverse Osmosis: The Most Comprehensive

By far the most comprehensive water purification option for rainwater, reverse osmosis is a very extensive water treatment option, second only to distillation in the purity of the final product. Reverse osmosis systems are generally only available to be installed in situ under the sink or at the initial water source due to their complex nature, this unfortunately makes them the best option, but also, the most difficult! The main advantage of reverse osmosis is that it can and will remove the vast majority of contaminants both inorganic and organic, even dissolved salts will be drawn from source water which explains its position as the most popular desalination technique worldwide!

Generally speaking, you can buy a suitable RO system to service a single tap on Amazon for between $200 and $300 USD, which you could install yourself if you are somewhat practical. However, if you are looking for a full household-type solution, it would be best to consult a local professional in your area as these large systems often require some serious pumps and high-pressure fittings.

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