Off Grid Water Harvesting: How To Install Rainwater Catchment (2024)

Water is the most important thing to consider when choosing a homestead. Without water, your off-grid property is virtually worthless. But how do you tap into a reliable water source for your off-grid homestead?

There are two ways to harvest rainwater on your property, through passive earthworks and water tanks. Earthworks include swales, ponds & basins that harvest rainwater in the soil. Water tanks actively harvest rain off of a roof into a catchment tank that can then be used in the home or for the landscape.

Read on to learn all about water and how to install an off-grid water harvesting system on your property.

Why Harvest Rainwater As Your Primary Source Of Water

There are a few ways to get water for your off-grid homestead, but not all are created equal. If you have enough rainfall and storage capacity, harvesting rainwater should be considered first. It is the best option for your pocketbook and the environment.

Obtaining your water through groundwater may seem like a great option, but if you consider the ecological costs, you may quickly rethink this option. Groundwater is ancient water, stored underground over centuries of accumulation.

In areas where too many wells have been dug, groundwater has been depleted in almost every case, leading to desertification and salty soils. This is not sustainable over the long run.

If you have a creek running through your property, you may consider this as an ecological option for your water source. Once again, the deeper you look into this option the more you’ll realize that it’s not necessarily the most eco-friendly one.

Drawing water off of a creek tends to have detrimental effects on the aquatic life within that watershed and in the most extreme circ*mstances may lead to lower flow which may lead to drought conditions further downstream.

That leaves us with the most precious resource that enters our homestead. Rainwater. Catching rainwater allows us to take a resource during its time of abundance and store it for later times of scarcity.

This not only decreases our impact on surface and groundwater resources but by saving the water for dry times you are helping regenerate water systems.

When most people consider harvesting rainwater, they instantly think of rainwater catchment tanks as the only way to do it. But there is another way, harvesting rainwater through the soil, or earthworks. We’ll go over both methods below.

Is It Legal In Your State To Harvest Rainwater?

Off Grid Water Harvesting: How To Install Rainwater Catchment (1)

You may have heard somewhere on social media that some states have made it illegal to harvest rainwater.

It is true that some western states have laws on the books since statehood that regulates rainwater harvesting. This is especially true when harvesting rainwater with Earthworks. Digging ponds in some places require environmental reviews and expensive permits in many arid states.

The vast majority of states have no laws, with many even encouraging it.

On Hawai’i Island where I live, the county actually put out a handbook on best practices for harvesting rainwater that many other states look to when deciding how to regulate water catchment in your jurisdiction.

It’s always important to check the laws and regulations in your state AND local municipality. While some states may allow water harvesting, there may be local jurisdictions that have more rigid requirements.

The most extensive resource I have found on which states allow water harvesting can be found from Acer Water Tanks.

Be sure to do your research, it may cost you thousands of dollars if you don’t.

Related: Can Rainwater Be Used For Showering?

How Is Rainwater Catchment Calculated?

Before installing your rainwater catchment systems, you have to know how much you can catch. It won’t do you any good to install a 10K gallon tank but are limited to 6K gallons worth of rainfall each year.

There are all sorts of equations and calculations to come up with a variety of numbers, but after installing close to 100 different water harvesting systems as a landscape contractor, I found it easier to remember just 2 rules of thumb.

For Calculating Rainfall Runoff Volume on a Catchment Surface:

You can collect 600 gallons of rainfall on a 1000 sq ft catchment surface

On a really big Scale:

You can collect 27K gallons of rainfall on a 1 acre catchment surface.

There’s no real need to learn all of the fancy equations if you can remember these 2 rules of thumbs. With these new rules in hand, you’ll be able to size your catchment systems accordingly.

Harvesting Rainwater In The Soil

Off Grid Water Harvesting: How To Install Rainwater Catchment (2)

This is where the real magic happens that often goes overlooked. Go back to the two water catchment calculations mentioned above. One catches 600 gallons of water from a small roof, the other catches 27k gallons on an acre!!

27,000k Gallons! Let that Sink in. Literally!

Harvesting rainwater in the soil is a powerful way to harvest water on a massive scale. For the dollar per gallon storage ratio, earthworks are also VERY economical as well.

The idea is to Slow, Sink and Spread the rainfall out into the landscape so that it can infiltrate into the soil instead of running off and washing away.

How do we accomplish this?

On contour swales. Rock Gabions in creekbeds. Keyline Design. Natural ponds. Sunken basins connected to rain gutters. Each one of these methods utilizes the earth and its ability to act as a sponge to harvest rainwater.

To design a system that harvests rainwater in the soil, I first start with the top of the watershed. This may be a roof on a suburban lot or the peak of a mountain. Observe the water and see how you can slow it down, spread it out and allow it to sink into the soil.

On a suburban lot, I will harvest the rainfall off of the roof into a water catchment tank with it’s overflow running off into sunken basins that catch the water. The basins may then lead into a series of basins or swales dug level to the slope of the ground. Think contour lines on a map.

A larger landscape may require slowing water down in creekbeds with rock gabion walls that act like beaver dams. Keyline Design is a method for large acreage to plow ditches into the soil on contour or slightly off contour towards the ridges, similar to swales.

For each scenario, I try and weave that water through the landscape as long as I can before it has to run off site.

While water harvested in the landscape is not necessarily made ready to use for your consumption, the plants in your landscape will be able to tap into it, pumping it up from underground in the form of fruit or vegetables.

Utilizing water in the landscape also has a side effect of hydrating the landscape well into the dry season, re-perennializing streams and raising water tables. I encourage you to add this to your water harvesting strategy.

Related: The BEST tool for laying out on contour swales is a Rotary Laser Lever, available from Amazon.


Harvesting Rainwater In Storage Tanks

Off Grid Water Harvesting: How To Install Rainwater Catchment (3)

This where we get the water that we’ll use for our household needs. Storing water in tanks is a primary way for many parts of the world to ensure access to water. In the Puna District of East Hawai’i, 95% of the people depend on rainwater catchment.

Many people think harvesting rainwater is only for those that live in wet climates, but people in dry climates can benefit as well.

By sizing a water tank for your household needs and taking into account the length of time between rainfall events, you might be able to harvest more than enough to get you through the dry times.

In any situation, harvesting even the littlest amount of rainwater will have a positive effect on the environment and on your pocketbook.

Let’s get into the various components that make up a rainwater harvesting system.

Roof Types For Rainwater Catchment

Harvesting rainwater at home starts with the water that falls on your roof. As we mentioned before, a 1000sq ft roof can catch 600 gallons of water from per 1” of rainfall. The average roof size in the US is 1700 sq ft, giving us well over 1000 gallons of water for each 1” received.

That’s a lot of water!

It’s best to capture the cleanest water possible, even if you do not plan on drinking it. By doing so you minimize the chance for clogged pipes or a corroded rain tank.

To capture the cleanest water possible, it is recommended that you use a painted galvanized steel roof. Painted galvanized steel does not rust as quickly as an unpainted galvanized steel roof would.

Tile roofs are full of debris, asphalt roofs have chemicals, even an all natural cedar shake roof will leach out chemicals and tend to catch more debris than you would like. Galvanized steel roofing is the only way to go.

Gutter Design For Rainwater Harvesting

The role of the gutter is to take the water that falls on the roof and catch it as it drains over the edge. It then leads that water down a downspout, preferably to a water tank.

The best gutters to use are seamless gutters made from galvanized steel. The plastic gutters that utilize connection points tend to back up, resulting in algae formation and debris blockage. The seamless gutters do not have any spots where water can get dammed up.

From the gutter, I like to transition to 2” PVC pipe as the downspout. This makes it very easy to lead the water from the gutter to your rain tank. It’s also easy to cut the PVC and attach a Leaf Guard on the downspout to help eliminate large debris before it enters the water tank.


Off Grid Water Harvesting: How To Install Rainwater Catchment (4)

The cistern is your water tank. Water tanks come in a variety of styles and sizes. You can utilize 55 gallon drums in a setup used by Bluebarrel Systems, a slimline tank for small side yards by Bushman, a larger plastic tank, a corrugated tank with vinyl liner, a ferrocement tank, an Underground Tank, even a bladder bag that can fit in short crawl spaces.

The tank you choose depends on how many gallons you want to harvest, space availability and price. I like to steer clients towards getting a tank that gets them the most bang for their buck. Forget about the vanity of how it looks and begin to see your water tank as security, just as important as any garden or money in the bank.

Related: Keep Water Clean In A Rain Barrel: The Essential Guide

Off Grid Water Pump & Pressure Tank

Once your tank gets full, you are going to need to find a way to send that water out into your household or landscape. You can accomplish this by gravity feed or mechanical pressurization.

To accomplish a gravity fed water harvesting system, you are going to need both slope and height. The ideal situation would be harvesting water off of a 2nd story roof and placing the water tank anywhere on the landscape that is just below the height of the 2 story roof.

This will give you the most elevation in which you can utilize gravity feed.

If you don’t have the height but still have elevation in your landscape, you can site your tank at the highest point and use a pump that utilizes daytime solar power to pump that water up to the tank, which can then be gravity fed during the nighttime hours or when the pump is not running.

If gravity fed is not possible but still want to pressurize your water, you can install an electric pump that leads to a pressure tank. This is how I do it at my homestead.

The water goes from my tank to an outlet line that leads to a small, energy efficient FloJet pump. This pump pressurizes in association with a pressure tank that keeps the water between 20 – 45psi.

It is a really simple setup that will last 5 to 10 years before replacement is needed.

You can get larger pumps than the one I mentioned, but your solar output and battery storage will have to be sufficient to power a larger pump. Often times it’s not worth it. My little Flojet pump provides more than enough pressure for our home.

Off Grid Rainwater Filtration Systems

Plumbed Water Filtration Systems

Once you have your water pressurized, it’s time to install the water filters. I use a standard homebased filtration system utilizing a 10 micron paper filter down to a 5 micron string filter. From there the water goes out to my shower, kitchen sink, hose and bathroom sink.

As long the guidelines above have been followed, another filter can be added to make the water drinkable.

I have an extra spigot at my kitchen sink that utilizes a Doulton Water Filter. The Doulton Filter is placed under the sink and can filter out 99.9% of any debris, pathogens or disease. This water is only for cooking and drinking.

My mom has a Quantum Water Filter which utilizes modern technology to filter out 99.9% of any of the harmful contaminants that may be present in the water. It takes no electricity and can be used on the whole house!

For an off grid homestead, this is the exact water filtration system that will fit your needs. It comes in at almost 5 times less than the average cost of a UV filter system, which is the industry standard for making rainwater drinkable.

The UV water filtration system utilizes a ballast, UV Bulbs (which require replacement yearly) and electricity, a lot of it. I never considered it viable for my off grid homestead.

With the advances in technology for the more passive ceramic based filtration systems, the UV Water Filtration is a thing of the past.

Water Filtration With No Plumbing Required

I get it. It can be intimidating to have to install a plumbed water filtration system into your home, even though the costs are low. That’s OK. You can go for an even more passive approach.

My family and I have been going backpacking for years. We are very familiar with off grid water filtration on a smaller scale. There is the Lifestraw which can be used to suck water straight out of a dirty river like a straw. We have a family version as a backup for our water filtration needs.

There is also the Sawyer Mini Filter which works in a similar fashion to the Lifestraw.

Back home on the homestead, a great option for on the counter water filtration would be the Berkey Water Filters. No other water filter has a better reputation than the Berkey Water Filter.

It works based on a gravity fed design in which the water runs through multiple layers of charcoal, sand, and rock to filter water.

I have used Berkey Water Filters in the past and have loved them. The water comes out tasting good and I have not once gotten sick from one of them.

Experiences With Harvesting My Own Rainwater

I have been harvesting rainwater for a long time as well as an installer of rainwater systems for over a decade. There is no other way that I would want to obtain my water.

It has been proven that water from municipal systems cannot be trusted. One only has to look to Flint, Michigan for an example of that. Even water from streams and from in the ground can be contaminated.

But water harvested from the rain? Besides the occasional acidity found through pollution in major metropolitan areas, rainwater is some of the cleanest water you can drink. It feels good to know that I have thousands of gallons of water that I can draw from at any time.

I did have to train my kids not to drink the water when they take a shower or brush their teeth, but besides that inconvenience, there are really no downsides from what I can see.

If you have the chance to install a rainwater harvesting system on your off grid homestead, take it. True freedom means that you can provide for all of your needs, with water being one of the most important.

Aloha! is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to This site also participates in other affiliate programs and is compensated for referring traffic and business to these companies.

Off Grid Water Harvesting: How To Install Rainwater Catchment (2024)


How do you install a water catchment system? ›

Tips for Installing a Rainwater Collection System
  1. Take roofing material into consideration. ...
  2. Choose a barrel designed for holding water. ...
  3. Locate barrel with safety in mind. ...
  4. Block up rain barrels several inches. ...
  5. Attach spigots and hose connections finger-tight only. ...
  6. Clean gutters periodically.
15 Mar 2020

How do you make a rainwater catchment? ›

How to Design a Rainwater Harvesting System
  1. Basic Rule for Sizing.
  2. Determine What the Captured Water Be Used For.
  3. Determine How Much Water Can Be Captured.
  4. Determine the Collection Surface.
  5. Calculate the Volume of Rainfall.
  6. Estimate Indoor Water Demand.
  7. Estimating Outdoor Water Demand.
12 Jan 2019

How is catchment capacity calculated? ›

Calculating your catchment capacity

Roughly speaking, 1 millimetre of rain over 1 square metre of roof equals 1 litre of water. This capacity can be calculated using the following formula: Annual rainfall (in millimetres) x Roof surface area (in square metres) = Roof catchment capacity.

How does a rainwater catchment system work? ›

Rainwater flows from the roof but instead of collecting in barrels via gutters, rainwater falls from the roof into a dug swale. The swale then channels the rainwater towards a holding area where the landscape plants or the vegetable garden utilize the diverted water.

What is a rainwater catchment system? ›

The rain will collect in gutters that channel the water into downspouts and then into some sort of storage vessel. Rainwater collection systems can be as simple as collecting rain in a rain barrel or as elaborate as harvesting rainwater into large cisterns to supply your entire household demand.

Where should a rainwater harvesting tank be placed? ›

Where should I site a rainwater harvesting tank? Siting your water tank properly will save you time and money. Ideally, you should site the water tank near to the downpipes of a rooftop with existing guttering. This will make installation much easier and reduce the pipework required.

How much does it cost to install rainwater harvesting? ›

Written by HomeAdvisor. Most homeowners pay $2,500 for water catchment system installation. A single rain barrel might only cost $120 while an extensive rainwater harvesting system can run up to $15,000. Rainwater tank prices largely come down to size, as well as the system setup.

How do you calculate rainwater harvesting capacity? ›

For calculation we take the following formula: mean annual rainfall in mm x area in m² x runoff factor = collected rainwater in litres. In our example this means: 450 x 120 x 0.9 = 48 600 litres.

How much rainwater can you collect from a roof? ›

Approximately 550 gallons of rainwater can be collected for every 1000 square feet of collection surface per inch of rain. To estimate amount collected in one year, take the square footage of your collection surface, divide by 1000, multiply by 550 and then multiply by the average annual rainfall for your area.

What is the formula for calculating rainfall? ›

Find the average volume of rain = Depth x radius x radius x 3.14. Find the area at the top of the bucket (this is the area over which the rain is collected). Divide the rainfall volume by this area to get the rainfall.

How do you calculate rainwater runoff? ›

For a given surface area such as a roof or yard, multiply the area by the inches of rainfall and divide by 231 to obtain the runoff in gallons. The factor 231 comes from the fact that the volume of 1 gallon equals 231 cubic inches.

How does a catchment tank work? ›

In these areas, homes are plumbed with a water catchment system. This is a large tank located on the property used to catch rain water for use inside your home. It's connected directly to your plumbing and creates a source for running water.

How long can you store rain water? ›

Generally, rainwater will become contaminated after about one week. You can prolong its lifetime indefinitely by keeping it out of the light and from animal and insect contact. In this article, I explain what causes rainwater to go bad and how it can affect plants.

What is a catchment system? ›

Water catchment, also known as water harvesting, is the process of collecting and storing rainwater. Water catchment systems collect water from rain gutters and use pipes to direct it to a storing drum, barrel, or cistern. Once collected, pumps move the water from the storing drum to where it needs to go.

Can I use rainwater in my house? ›

Rainwater might not be safe for household use without additional treatment. Before using collected rainwater for drinking, bathing, or cooking, consider whether treatment is needed to make it safe. Testing the water can determine if there are harmful germs, chemicals, or toxins in it.

How do you store rainwater long term? ›

Rainwater that is being used to water plants can be stored for one week before it becomes contaminated and can't be used. It can be stored for longer if stored in a sealed, darkly colored container. Check for mosquitoes and algae before using rainwater to water plants.

How is rainwater harvested for home use? ›

Best Ways to Collect Rainwater - YouTube

How do you make a homemade rain barrel? ›

  1. Step 1: Drill a Hole. Drill a hole a few inches above the bottom of your trash can. ...
  2. Step 2: Attach and Seal the Spigot. ...
  3. Step 3: Make Entry and Exit Holes. ...
  4. Step 4: Screen the Top. ...
  5. Step 5: Place Your Rain Barrel.
3 Mar 2022

Do rain barrels have to be connected to downspout? ›

Rain barrels are usually positioned below the downspout of a roof gutter; however, you can still use a rain barrel if your house doesn't have gutters. You can also attach several rain barrels together with a simple connection kit.

Do it yourself rain gutters? ›


Are rainwater tanks cost effective? ›

Great potential savings

When your rainwater tank is properly installed and plumbed into your home, it could save up to 40% of your drinking water supply. That could mean $200 a year off your water bills.

How do you install a rain barrel? ›

How To Install A Rain Barrel - YouTube

Does rainwater harvesting save money? ›

Lastly, rainwater harvesting can save money by significantly reducing your water consumption and therefore lowering your water bill. It can even help you save money on your energy bill, as rainwater harvesting systems are extremely energy efficient and cost very little to run.

How much does a water catchment system cost in Hawaii? ›

Average Cost of a Rainwater Catchment System

Costs typically range between $1,000 – $5,000 for a roof top collection rainwater harvesting system.

How do you divert water from a downspout to a rain barrel? ›

Simple, best way to connect rain barrel to downspout - YouTube

How much does it cost to install a rain water system? ›

The cost to install a rainwater collection system varies based on the type of system, materials, and needed labor. The national average cost ranges from $1,000 to $3,500, with many homeowners paying about $2,500 for a dry system with a 5,000 gallon polyethylene storage tank installed.

Can you drink rain water in Hawaii? ›

For health and safety reasons, in general, the Hawaii Department of Health does not recommend using catchment water for drinking or preparing food. County water spigots can be used instead as a safer water supply.

Are rainwater tanks cost effective? ›

Great potential savings

When your rainwater tank is properly installed and plumbed into your home, it could save up to 40% of your drinking water supply. That could mean $200 a year off your water bills.

How do you make a homemade rain barrel? ›

  1. Step 1: Drill a Hole. Drill a hole a few inches above the bottom of your trash can. ...
  2. Step 2: Attach and Seal the Spigot. ...
  3. Step 3: Make Entry and Exit Holes. ...
  4. Step 4: Screen the Top. ...
  5. Step 5: Place Your Rain Barrel.
3 Mar 2022

Do rain barrels have to be connected to downspout? ›

Rain barrels are usually positioned below the downspout of a roof gutter; however, you can still use a rain barrel if your house doesn't have gutters. You can also attach several rain barrels together with a simple connection kit.

What happens when rain barrel is full? ›

When the rain barrel is full, the diverter shuts off, and the rainwater will simply flow through the gutter like it normally would.

What is the easiest way to filter rainwater? ›

A Filter with a stainless steel mesh is best and, ideally, at this stage you should be looking to filter the water to at least 1mm (1000 micron) - the finer the better. The Rainwater Filter should be installed where it is easy to inspect for maintenance and should be easy to clean.

What is the best filter for rainwater? ›

Activated carbon: All water will carry with it its own taste and odor, and rainwater is no exception. To get the best water quality possible, as well as the best tasting water, a granulated activated carbon (or “GAC”) filter is a must for any system.

How long can you store rainwater for drinking? ›

Generally, rainwater will become contaminated after about one week.

How much rain does it take to fill a 50 gallon rain barrel? ›

It's common for about 1/8" inch of rain to fall each hour during a moderate rainstorm. That means that a 500 square foot roof can fill a properly installed 50-gallon rain barrel in about one hour.

How high should a rain barrel be off the ground? ›

Barrel(s) should be placed high enough off the ground – generally a foot or more – to be able to fill a watering can, or attach a hose and get good pressure. Place the barrel(s) on the base with the intake hole closest to the downspout. square feet of roof can produce over 600 gallons of water!

What are the disadvantages of a rain barrel? ›

The main disadvantage is their small size which really limits the potential rainwater collection volume. To increase the rainwater collection capability, you would need to link multiple rain barrels together which increases the connection points and the opportunity for failure or leaks.

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