How to Collect Rainwater: Harvesting Guide

Collecting Rain Water

In case you may have not known, WATER is the most abundant natural resource on planet earth. While most of it may be salt water, when it rains, it is natural, purified water which is the perfect source for consumption and a secondary source for watering your garden (an essential food source).

While rainwater collection may be an excellent way to save on your water bill, it actually is a much better way to consume water. Since things such as fluoride, chlorine and other chemicals are simply NOT found in rainwater. Keep in mind, a water filtration system is a highly recommended addition to ensure its safe to consume.

By collecting rainwater, you’ll begin to contribute towards a cleaner, more sustainable environment. NOTE: Do keep in mind that not everywhere you can legally collect rainwater (as crazy as that sounds), do check your local laws to ensure you won’t have someone coming after you. 


Alright we’re going to dive deep into the steps you need to follow to ensure you are harvesting rainwater the RIGHT way. Before you proceed to buying the items you need, be sure to read each step below a few times to ensure you know exactly what is required.

Roof Water Funnel Installation

1. Using Your Roof As The Water Funnel

If you want the easiest way to collect water, use your current roof as the way you’ll funnel the water directly into a barrel. This is by far the most commonly used catchment area.

Primarily because it is already equipped with gutters and other fixtures which will guide rainwater run-off into a specific direction. To ensure you get the most water run-off, it’s recommended you designate a downspout directly beneath a steep part of where water tends to accumulate. This will ensure you get as much rain water funneled down towards a designated location as possible.

As mentioned before about the legality of collecting rainwater, whichever decision you make, if you decide to go through with it… pick an area behind or at least to the side of your home to keep your whole rainwater collection system hidden from view.

Properly Channeling Runoff​​

2. Properly Channeling Runoff​

As mentioned above about gutters, most homes are equipped with them, and that is good. The standard sized gutters are 5” in width at the top and 3” in width at the downspout. This isn’t always the best size as some roofs have greater surface area, in which case replacing the gutter with 6” in width at the top, and 4” in width at the downspout is more ideal.

Now, not all roofs are created equally. In fact, the most effective type of roof would be one made of sheet metal. The surface is suited BEST for collecting rain due to its low friction level for water to slide down. When it comes to wood shakes, asphalt shingles and clay tiles, you are prone to mold, moss and algae growth… but that isn’t a deal breaker as long as you take care of them appropriately over time.

First Flush​​

3. First Flush​

When mentioned about keeping your system hidden from view, a “first flush” system is an add-on which helps to keep away roof debris from entering your water collection tank. This is an optional thing to install, but is very helpful when there. 

How it works is quite simple, when water goes in, it accumulates at the bottom of the “first flush” water diverter chamber. This flushes out the first few gallons of rainwater and most debris which would be found at the beginning of rain. When the chamber is full, it raises the ball inside to the top to redirect water towards the original direction which is your water collection tank.

At the bottom of the chamber, there’s an outlet which lets water pass through with a built-in filter. When this part starts to get clogged up, you can disconnect, clean out and place back. Have a look into the animation below to see exactly how this process works. A complete kit (which uses pvc pipes) can be found on Amazon here for about 35 dollars.

Collecting the Water​

4. Collecting the Water​

So the downspout now must feed directly into a container where you’ll be storing all of your water, but what do you use as a container? 

Good question, and the answer is quite simple, you use a plastic rain barrel. This is the most common method of harvesting rainwater.

You can find a 50 gallon (190L) plastic barrel at you our local hardware store for 50-75 dollars, so it isn’t much. At most hardware stores and gardening centers, you’ll be able to find specifically-designed barrels with built-in filtration screens and spigots, this ensures you get rid of small to medium sized particles which come down from your gutters, from your roof.

If you aren’t willing to spend the money to buy a designated barrel… you can use something found around your house, such as a trash can. No matter what type of container you use, please ensure you use something that isn’t opaque. By blocking out sunlight from going through the barrel, you prevent mold and algae from growing… and that is crucial for a health source of water.

Elevate the Barrel to Increase Water Pressure​​

5. Elevate the Barrel to Increase Water Pressure

This part is quite easy and only requires a few cinder-blocks to have done properly. Assuming you have a shovel, what you need to do is first dig a shallow trough at your designated catchment area, and place cinder blocks inside until the top of them matches the surface evenly (no lower).

 If right at the surface, you cover with dirt to conceal them. After that place a few more cinder blocks on top to elevate your rain catching container. As you raise the container, it’s easier to position your container beneath the spigot where the water comes from.

Water Filter

6. Determine Where Your Water Will Go​

 If right at the surface, you cover with dirt to conceal them. After that place a few more cinder blocks on top to elevate your rain catching container. As you raise the container, it’s easier to position your container beneath the spigot where the water comes from.

 We recommend you look into the Burkey Water Filtration System because it has some of the best filtering against fluoride, chlorine, lead, arsenic and much more. However, you can use any other filtering system you find suitable for your needs.

If you decide to use the water for gardening, filtration becomes unnecessary as your plants will receive the same type of rain water if you didn’t collect it. You can run a hose with an electric water pump and water your garden with no further steps needed.

How Much Will This Entire Setup Cost Me?​

An excellent question, let’s break it down to see exactly the costs associated with building your system. For example, we will use Amazon prices from their online marketplace.

  • Cinder Blocks $1.40/each x 10 = $14.00 (can be found at HomeDepot & Lowes)
  • 50 Gallon Rain Barrel with Brass Spigot = $90.00
  • First Flush Kit = $35.00
  • 12 Volt 1-2 GPM Water Pump = $25.00
  • Flexible Water Hose = $30.00

Rough Estimate is $194 USD, let’s round it up to $200. By all means though, with creativity and budget shopping… you can make this much less.

Frequently Asked Questions Answered in Greater Detail​

Is It Legal To Collect Rainwater?​

You’ll hear stories of being being jailed by collecting rain water for their own personal use. One story about a man from Oregon being jailed for 30 days after being caught collecting rain water may scare many people… but not everyone mentioned the truth about the REAL reason why he was in jail for 30 days. He actually diverted water from nearby creeks and dams to amount a reservoir to fill almost 20 olympic-sized swimming pools. This type of thing likely disrupted wildlife, and made it very illegal to do.

However, this is a super rare case and does not mean one cannot harvest rain water in Oregon for instance. In fact you can, but just not to that degree as mentioned with the man.

A similar misunderstanding about rainwater collection laws in Colorado have caused many to believe that state outright bans collection of rain. That was true prior to 2009, since they have highly strict laws regarding this matter. After 2009, the state introduced laws which made it LEGAL to use rooftop collection systems and even rainwater retention basins on new development sites.

Quite a few states are leading the way with rainwater harvesting, some even providing incentives and rebates for buying the necessary equipment. The following states are: Texas, Hawaii, Alaska, California, Arizona, Florida, Ohio, Rhode Island, Illinois and U.S. Virgin Islands.

How To Filter Rainwater for Drinking?​

As you read above, the first line of defense from outside contaminants such as leaves, dirt, bird droppings, dust, rocks, bugs and among other things, is to have a mesh net installed inside the gutter. From there you’ll have a first flush system to further get rid of unwanted materials, and then have the water make its way down towards the water tank.

From the water tank you can run the water through a fine mesh filter, and then through a cartridge style filter which will further remove contaminants. If you’d like to further filter the water, you can even use a Ultra Violet Light filter which will further kill any pathogens found in the water.

How To Collect Rainwater WITHOUT Gutters?​

This can be done one of three ways, you can either create a giant rain-saucer which funnels water directly into the a rain barrel, you can use a rain catching tarp which is even more effective, OR you can build a separate roof which will be created specifically for funneling water into a rain barrel. The latter being the most time consuming and expensive method.

Is Rainwater Safe To Drink From The Sky?​

Yes absolutely, it is as safe as your tap water or bottled water (which is often filtered tap water). The difference between rainwater and water you’ll find from the tap… is that rain has no added chemicals by nature.

What Are The Main Benefits of Harvesting Rainwater?​

If you filter your rain water, you can drink it and if you don’t, you can use it for essentially anything you can put your mind to which doesn’t involve human consumption. From washing your car, cleaning your house, washing your pets, and to watering your garden. The options are limitless really, after all its water directly from the sky!

Can I Store Rainwater Underground?​

Yes, you absolutely can. This is often done by those who have a big water container (1,000 gallons+), this requires either a small tractor to DIG or a shovel with a few hours of dedication.

What Can You Do With Rainwater?​

If you filter your rain water, you can drink it and if you don’t, you can use it for essentially anything you can put your mind to which doesn’t involve human consumption. From washing your car, cleaning your house, washing your pets, and to watering your garden. The options are limitless really, after all its water directly from the sky!

How Long Can Rainwater Be Stored?​

Rainwater does not have a set shelf life, as long as it is away from sunlight… it is likely to be fresh to drink or at least use for other purposes. Remember, microorganisms and algae can grow in water that is exposed to sun light. Properly keeping an eye on your stored water will ensure you have nothing harmful growing.

What Is The Formula For How Much Rainwater I Will Collect?​

Alright, here’s the formula for how much rainwater you’ll actually collect from your roof. We are going to measure the roof in square feet (sq.ft).

Lets say the average area size of a roof is around 1,500 square feet and you receive 25″ inches of rainfall every year, that means your roof will collect 23,362.5 gallons of rainwater. That is about 1,946.87 gallons per month to use or about 64.8 gallons of daily water to use.

Formula: inches of rain X square feet of roof area = gallons harvested
Example Given: 25″ inches of rain X 1,500 sq.ft = 23,362.5 gallons harvested

Wrapping Up, Thoughts?​

Hopefully you found this how-to article very useful, as I have done quite a bit of research to bring forward what you see here.

Personally, I think this is something everyone should be doing to not just save money… but to also drink healthier water. I am a firm believer our modern water system has chemicals which serve NO true benefit to our bodies and in fact cause harm in the long run.

Whether you live in a BIG city, SMALL city, a town of some kind, or off-grid, this is a MUST for your wallet, and your health.