I’m all for harvesting rainwater – itʻs how I get my water on my off grid homestead. But harvested rainwater is not safe to drink. Even if you use a first-flush system (which you should!) and filter out bits of leaves and other debris, you’ve still got to disinfect your water before consuming it. 

The cheapest way to purify water would be through solar distillation, as it is basically free except for the one-time cost of plastic. However, that would be for small scale applications. For larger, whole house applications, the cheapest way to purify water would be with a UV water filter.

I always thought that something like boiling water wouldʻve been the cheapest way to purify water.  Except I’ve got a secret: it’s not. 

Nope, there are cheaper ways that use less energy and effort on your part to purify water.

Treat Stored Rainwater

Remember, you should treat any collected rainwater you plan to store, even if it isn’t for human consumption. Rain water left in galvanized tanks can grow algae from any microbes or bacteria that made it past your filters. 

For the purpose of this post, purification means making the water safe for human consumption, aka: potable water.

This post is a list of incredibly cheap ways to purify water, less than a penny per gallon of water. 

However, I wouldn’t suggest these be your long-term solutions for purifying your drinking water, but they could be a good way to get started until you’re ready to invest in something a little easier and more convenient for your off-grid homestead, long-term.

What does “purified” water mean?

As mentioned in my other post about Boiling Rainwater, you need to clean rainwater to remove dust, pathogens, parasites and bacteria and chemicals. 

So, purified water means water that is safe to drink, not necessarily water that has had all chemical components and microbial bits of dust removed.

Some methods of purifying cannot remove “forever chemicals” from rainwater. 

For this post, keep in mind that I’m aiming for ‘safe to drink’ rainwater, not necessarily something that has no trace amounts of metal or chemicals in it. In fact – some of the methods use chemicals as disinfectants.

So, review these ‘cheap methods’ with that understanding, and decide for yourself if these options are a short-term or long-term solution for your off grid homestead.

Cheapest Forms of Water Purification

Let’s get to it, the cheapest ways to purify water so it is safe to drink:

  • Solar (Solar water disinfection (SODIS)
  • Chemical Disinfection
  • Water Filters
CostFilters DebrisEliminates Microorganisms
Boiling Water$0.10 – 0.35 PER GALX
Solar Water Disinfection$0.00 PER GALX
Chemical Disinfection$0.002 PER GALX
Ceramic$0.005 PER GALXX
Sand/Gravel Filter$0.005 – 0.01 PER GALX
WaterDrop Filter$0.008 PER GALXX
Straw Filter$0.04 PER GALXX


Now, boiling is not one of the cheapest methods for purifying water, but I mention it straight-off because its a common misconception that it is, and might be the first method you thought of, too. 

First of all, you can only purify small quantities of water through boiling and it requires a decent amount of energy and fuel (as well as attention and time) to boil water for 3-5 minutes.

This isn’t to say you can’t or shouldn’t boil water to purify it for drinking purposes. It’s an easy solution if you’re in a pinch, but, don’t be fooled – it is not the cheapest method.

Estimated Cost: it costs an estimated $0.10 – 0.35 to boil one gallon of water on a regular stovetop, or a half a gallon in an electric kettle. 

Surely, if you’re using a gas stove or running a conventional stove off of generator power, it’s going to cost you more for every boiled gallon of water, making this actually one of the most expensive methods for purifying water.

Pros: Almost everyone who is living off-grid has access to a pot and a stove. 

Cons: Boiling does not remove bacteria or pathogens from the water, it merely kills them, rendering them harmless. It also does not remove dust particles, trace metals or chemical components found in rainwater.

You can only boil small quantities of water each time and it can end up being expensive.

Solar Water Disinfection

Solar Water disinfection is also known as SODIS and uses, you guessed it, the power of the sun to disinfect water. 

Basically, you put rainwater into plastic (PET) bottles and leave them in full sun for 6 or more hours. Both the heat of the sun and the natural UV light will kill pathogens and other biological contaminants.

Pros: Basically free, if you use clean, recycled PET bottles (old soda bottles, water bottles). Also, this approach doesn’t require your attention or effort to purify the water, just that you make sure the bottles are in direct sunlight for a full day.

Cons: Of course, like with boiling, this method does not remove pathogens or filter your water for metals or chemicals, it only kills off dangerous bacteria or parasites. It doesn’t filter out dust or address chemicals in the water, either.

Also, you can only purify small quantities of water at a time – something like 2 liters in each bottle, max, to ensure the water gets all the UV rays of the sun.

Also, it requires full sun for daylight hours, which means, during rainy periods, you may need a backup plan for purifying your rainwater.

Finally, there is no guarantee of ‘residual’ protection with this method, meaning you need to consume the water within a day or two – don’t store it.

Chemical Disinfection – Chlorine

Yes, this is what is exactly what it sounds like: cleaning your water with a few drops of chlorine bleach. 

If that freaks you out, keep in mind that the most common form of water treatment used by government water systems is chlorination, so if you haven’t always lived off-grid, you have probably had chlorine in your drinking water at some point.

In tiny amounts, bleach will kill off any pathogens and viruses, while still being safe to drink. 

An easy measurement is 1 gallon of water per 16 drops of unscented, chlorine bleach (no dyes or other additives). Just use an eye dropper (found at pharmacies in the first-aid section) to count the number of drops. Then wait about 40 minutes or so, and your water is safe to drink.

Estimated Cost: Because bleach is pretty cheap ($5.00 for a small jug) and let’s say, it takes you 5 years to finish one jug, you’re looking at a meager $0.002 per day in clean water. Even if you ‘speed’ through the jug of bleach in 2 and a half years, that’s still just $0.005 a day in disinfected water.

Pros: Incredibly cheap, very easy and fast.  It is effective against pathogens and parasites.

Very easy to do, and the bleach won’t expire like filters do.

Cons: The water can taste bad after and this treatment method doesn’t address chemicals, heavy metals or other microbial materials in your rainwater.

Ceramic (Clay)

A classic ceramic filter is a simple, natural filter that removes parasites and bacteria for safe drinking water. 

Many ceramic filters utilize natural materials, including sand, sawdust or coffee grounds (some burn off during the firing process). 

These filters work really well and are inexpensive (and estimated at $0.005 per gallon of water, with filters lasting from 3-5 years). Here’s one for approximately $23.00 sold by a company in Uganda.

But, let’s be practical here, they are difficult to find available for purchase in Hawai’i or for reasonable shipping rates to other locations. In this case, you’ve got to look at making your own. Maybe it can turn into a side hustle?

Here is an awesome video showing to make your own basic ceramic filter, using easy-to-source and inexpensive materials. Making your own ceramic filter has its own advantages and disadvantages.

Estimated Cost: $60.00 – $70.00 upfront investment for filter materials to make your own filter that will last for 5 or more years. You are looking at around $0.03 per day (not per gallon) for water, when using a ceramic filter, and the amount of water you do is pretty much unlimited during those 3 or 5 years.

Pros: Requires no energy to filter water, just pour it in and wait approximately an hour for the water to pass through the filter.

A natural means of purifying water that lasts for years without much maintenance from you (you might clean your filter every 3-6 months with a quick wash and scrub-down).


Difficult to source in Hawai’i or North America.

You can make your own, but is time-consuming and you have to purchase the basic materials (mostly sifted potter’s clay) and then ask a pottery shop or artist if you can fire your filter in their kiln before use.

If you make your own, you have to wait for the clay to dry, meaning this isn’t an option you can use immediately, either.

Water Filters

There are plenty of filters out there, sometimes known as ‘counter top filters’. A lot of the more popular ones sold online are for potable tap water and they just remove some minerals or metals and improve the taste of the water. 

That’s not what I’m talking about here. I’m talking about a DIY slow-sand, or sand-and-gravel filter. 

Sand and Gravel Filter

You can easily make your own sand and gravel filter (also called a “slow sand filter”) with just a few items from a local hardware store, or, if you’re lucky, from a nearby quarry – they might just let you get them for free because you need such a small quantity.

The filter is made up of layers of small stones (gravel) in various sizes, sand, and a central layer of charcoal, with a piece of mesh in between the charcoal and sand. You can make this filter using a blue plastic rainbarrel, and even have harvest rainwater directed straight into the barrel/filter for convenience.

Estimated cost: based on the CDC’s estimated cost to build a sand-and-gravel filter (between $15-$60), we can conclude that a filter with a 10-year lifespan costs around $0.005 – 0.01 per gal for water.


Requires no energy or fuel to filter water, can direct rainwater straight to the filter to make less hassle for you. This process also boasts to remove mangese, tubidity and iron as well as some major pathogens from the water.

It’s a relatively fast method of filtration, in less than an hour, and it has a long lifespan – up to 10 years.


It is at the bottom of the scale in terms of effectiveness against viruses. According to the CDC, 

“[The] Slow sand filter lab effectiveness studies with a mature biolayer

 have shown 99.98% protozoan, 90-99% bacterial, and variable viral reduction. 

Field effectiveness studies have documented E. coli removal rates of 80-98%.”

It does not filter chemicals or offer risidual protection (so you should not store water long-term in a sand and gravel filter).

WaterDrop Undersink Filter

Now, if you’re looking for something to buy and save yourself the hassle of making a filter, then this under-the-sink filter is for you. 

The WaterDrop Undersink Filter easily attaches to your kitchen sink’s plumbing and has up to 0.01 micron filtration (which is sufficient for parasites or pathogens like giardia and cryptosporidium.

What I like about it, too, is that it cleans chlorine and other chemicals, but doesn’t remove ‘good minerals’ in your water.

Estimated cost: The filter should be replaced after 1 year, or after filtering 8000 gallons of water making the cost of the original investment of $71.00 either $0.008 per gallon of water. But let’s be reasonable, you probably will replace the filter after a year, before you’ve reached 8000 gallows, making the cost higher. 

$65.00 per year for replacement filters factors out to $0.19 per day, which is still cheaper than boiling water.

Personal Straw Filter

Another option is to use a personal straw filter, most popularly known as a “Life Straw”. You could simply pour collected rainwater in a glass and drink it through this straw which filters out microbial bits of debris as well as pathogens.

One of the cheapest options I’ve seen is this “Nature Nova” which allows you to purify 1500 liters (396 gallons of water) between the two straws. 

Estimated Cost: At the cost of $19.00 for the two-pack, you’re looking at $0.04 per gallon of water, which is still preferable to boiling.

Pros: Simple, effective and requires no work on your part, except to suck through a straw.

Cons: It can only be used by one individual at a time, meaning it’s not a good option for families or couples.

Final thoughts:

One option is to combine these water purification methods to get the best overall drinking water. 

For example, you can chlorinate 2-3 gallons of water, and then run it through your sand-and-gravel filter, which will help remove some of the poor taste associated with bleach as a disinfectant.

It won’t make the overall cost much higher, and it won’t damage your filter, either, making it one of the cheapest options for purifying water, which also doesn’t have such a strong odor or taste.