Sumo Gardener

Rainwater Tanks | Complete Guide

A quality, American-made rainwater tank can be an incredibly worthwhile investment. Connecting one or more tanks to your home's roof gutters ensures water runoff is stored for further use.

The rainwater can then be used for gardening, washing, flushing and even as potable water, which refers to water suitable for drinking. The only limits on the potential are how far you're willing to take it and where you're located in the United States.

We've compiled this useful guide to rainwater harvesting and rainwater tanks to indicate the benefits, requirements, and laws surrounding the topic, including everything needed to start collecting rainwater.


What is Rainwater Harvesting?

What is Rainwater Harvesting

Put simply, rainwater harvesting is the process of capturing rainwater for further use. In residential circumstances, rainwater harvesting sees homeowners install rainwater tanks by the house.

These storage tanks connect to the roof and guttering, so runoff flows to the tank instead of the stormwater drain. There are many uses for the water both inside a home and across the property. 

For example, rainwater harvesting is used extensively in rural locations like farms and remote communities and by citizens in countries with limited access to running water.

The age-old process of harvesting rainwater is rising in popularity thanks to the environmental and cost-saving benefits.

With a push towards more sustainable practices, collecting rainwater is one of the easiest ways to enhance your home’s eco-friendly qualities.

Benefits of Installing a Rainwater Harvesting System

Installing a rainwater tank on your property is a no-brainer. This is a great way to become self-sustainable while limiting your impact on the environment.

There's also a sense of satisfaction that comes from harvesting your own water and using it to live off of the land. There are many practical benefits. Here are four of the most rewarding:

Reducing Water Bills

According to the United States Environmental Protection Agency (EPA), the average American family uses more than 300 gallons per day.

With water priced at around $1.50 per 1000 gallons, you could save up to $162 per year by relying on a rainwater tank as your primary source of water.

Of course, this would require a large tank and plenty of rainfall, but there are discernible savings to be had regardless of location.

Benefits of Installing a Rainwater Harvesting System

Emergency Supply

Hurricanes, earthquakes, wildfires. If disaster cuts you off from the local reservoir or water supply, a rainwater tank can act as backup, providing you with enough water for drinking, washing and flushing.

In the case of a house fire, the water along with a suitable hose and pump could be used to extinguish the flames.

Limiting Floods

Capturing rainwater during a heavy downpour can reduce the flow and volume of storm water runoff. This reduces the strain on the sewers and limits the potential of water flooding your property. Both of which can require costly repairs.

Bypass Water Restrictions

During drought conditions, local authorities may impose water restrictions to reduce the strain on reservoirs. Having a rainwater tank creates a workaround where you can access additional water beyond the limit of the restrictions.

The more tanks used in the community, the less strain on reservoirs. With a seemingly endless supply of drinking water waiting for us at every faucet, it's easy to take water usage for granted. 

But it doesn't take much time, money or effort to reap the benefits of harvesting water. It's essentially a free-to-use supply that comes with the satisfaction of living off the land.

Collect Rainwater for Indoor or Outdoor Use?

Benefits of Installing a Rainwater Harvesting System

The Office of Energy Efficiency & Renewable Energy states that typical uses of rainwater across the United States include landscape irrigation, washing clothes, filling ponds and flushing toilets.

However, there's no limit to its uses, as the rainwater can be consumed with additional treatment via the appropriate chemicals.

Chlorine, hydrogen peroxide and silver nitrate can be added in specific formulas to kill bacteria and improve the water's quality, making it suitable for drinking.

Chemical solutions are available in liquid and tablet forms with the exact quantity or volume depending on the size of the tank. However, it's worth noting that the costs of treatment chemicals can outweigh the price of potable water. 

So it's best to reserve tank usage for washing and flushing if possible. As the rainwater is collected from your roof and gutters, they must also remain clean and free from dirt and debris. 

A professional plumber can connect a rainwater tank to your home via a pump so that it's pressurized for use across your faucets, shower head and toilets. A plumber can also fit your rainwater tank with a first flush diverter that protects your water supply's cleanliness. 

A first flush diverter sends the first flush of rainwater along with dirt and organic particles to the storm drain, so the cleaner second flush starts filling your tank. 

The collected rainwater can always be used across the garden and for other outdoor purposes with little to no treatment.

Advantages of Rainwater over Tap Water in Gardening

There is a reason why gardeners often say, “It really needs to rain.” Even if you regularly water your plants through a hose or sprinklers with tap water, your flowers or crops would still not look as lush and healthy compared to when they’ve been nourished with several days’ worth of rain.

There are many reasons why rain water is more beneficial for plants than tap water.

Advantages of Rainwater over Tap Water in Gardening

Rainwater vs Tap Water

Tap water contains chlorine, which is necessary for disinfection, as well as trace amounts of fluoride, salts, calcium, magnesium, and sodium.

All these elements are known to be toxic or harmful to plants. For instance, chlorine toxicity is real for most plants; an indication of a plant exposed to excessive amounts of chlorine is burnt leaf margins.

Even fluoride, which is put in our water to prevent cavities (provided we each drink one glass per day), is especially toxic to indoor plants, pines, and fruit trees.

Some symptoms of fluoride toxicity are burnt, spotted, or discoloured leaves and stressed fruit. In addition, calcium, magnesium, and sodium do a bit of harm to plants.

The white substances on the leaves of your plants are calcium and magnesium sediments, while sodium has been proven to be toxic to plant tissues.

Also, when it reaches the ground, sodium leaves damaging effects on the structure of the soil as it disperses beneficial aggregates of soil particles and creates cracks on the ground.

Rainwater has more benefits for plants than tap water. Firstly, it makes plants more green and lush because of the nitrate and ammonium elements found in rain. This element is absorbed by the plants through its roots and leaves.

Avoid Waterlogging

When you accidentally overwater your plants with tap water (it causes anaerobic soil conditions and may cause the roots of your plants to rot), it causes waterlogging.

However, this is not so much a problem with rainwater as rainwater has an abundance of oxygen, which guards the soil even when it is saturated.

Rainwater also contains carbon dioxide, which gives rainwater an acidic pH. When it reaches the soil, helps to unlock micronutrients locked up in the soil such as manganese, copper, zinc, and iron.

(This kind of rainwater is different from acid rain, which is caused by an excessive amount of pollutants in the air.)

The above benefits are just some advantages of using rainwater instead of tap water in gardening. You can also save on monthly water bills and use rain for your other household tasks like doing the laundry, flushing the toilet, and washing your car.

If you’re looking into storing rainwater for your household needs, the quality containers such as those provided by Rain Water Tanks can help you. Storing rainwater is worth investing for your plants and water bills. 

Types of Rainwater Tanks

There's a wide range of rainwater tanks and rain barrels available, so there's an option to suit all homes and properties. It's estimated that a quality tank will last 20 years and potentially longer if buried underground. 

However, repairs and maintenance become much more difficult if positioned underground. Alongside a house is the most practical position, atop a level concrete slab or compacted earth. 

It's also wise to go with an opaque tank which blocks out sunlight. This reduces the likelihood of algae bloom forming and contaminating your tank.

Types of Rainwater Tanks

Plastic Water Tank

Plastic water tanks are becoming the new standard residential rainwater tank favored for their price point, non-corrosive materials and wide range of available colors.

Modern plastic tanks are made using thick polyethylene that's both FDA and NSF approved for potable water storage and they are typically constructed in one piece to limit the risk of leaks.

These tanks are available in various shapes and sizes, including flexible bladder tank options for easily fitting under a home or in tight spaces.

Metal Water Tank

A metal water tank is constructed from steel, using either flat or corrugated sheeting. A food-grade interior lining ensures the water remains contaminant-free even if the tank were to rust. 

There are galvanized and stainless steel options available. Galvanized tanks are more affordable, but stainless steel does guarantee a longer lifespan.

Installing a Rainwater Harvesting System

Fiberglass Tank

The fiberglass tank is a lightweight, more affordable alternative to polyethylene plastic, but it is also rigid and more prone to damage. Modern tanks are built from a Glass Fibre Reinforced Plastic with food-grade interior lining to maintain water quality.

Many fiberglass tanks are transparent and so must be buried or positioned out of direct sunlight to limit algae bloom growth.

Fiberglass tanks are available in large sizes, making them well suited to farms and industrial sites.

Concrete Water Tank

Concrete water tanks are often found on farms or industrial sites. They don't match the aesthetics of homes. Instead, they are custom-built for large areas and are often buried to save space.

Concrete tanks are the most expensive rainwater tanks, but the benefits include long lifespans and they naturally keep water cool. 

Rain Barrels

Rain Barrels are the most common storage solution used for collecting rainwater. These cheap, portable alternatives are often constructed from polyethylene and positioned directly beneath a downpipe and rain head, so water flows directly inside.

The captured rainwater is typically reserved for gardening as there's a lot less usable water than the other tank options, and it's less worthwhile to treat such a small quantity for drinking.

Rain barrels are ideal for those looking to explore the world of rainwater harvesting without committing to a larger water storage tank. Also, for renters looking to be more sustainable.

Rain Barrels are the most common storage solution used for collecting rainwater

Choosing a Water Tank for Your Property

There are numerous water tanks on the market these days, though, so if you’ve never made this kind of purchase before, it can be hard to decide. Follow a few tips, and you should find the process easier and quicker.

Know How You Want to Use the Water

To choose the right water tank, get clear about how you want to use the water you collect. If you purely want to take the water from your tanks and use it for outdoor tasks, such as watering the garden, washing the car, or cleaning outdoor areas, for instance, you can choose and install whichever product you like. Most water tank suppliers could install it for you, too.

On the other hand, if you plan to use the collected water in your hot water system, washing machine, dishwasher, toilets, or the like, a licensed plumber will have to carefully connect the tank(s) to your main water supply. If you want to be able to use the water for drinking, there is even more to think about.

Rainwater Tank Regulations

Water Tank Regulations

Different governments and municipality offices have different rules and regulations that apply to water supplies in their regions. As such, you must do specific research to find out what is and isn’t allowed in your local area.

You may need to submit a development or building application to add any water tank to your yard, or you may need to for some types but not others.

Plus, there are typically very stringent rules around drinking collected rainwater, as well as issues regarding mosquito breeding near or in water tanks.

You may need to adhere to set rules regarding things like where a tank can sit, its height or color or type, how it’s labeled, or even noise regulations for its pump or other factors.

Furthermore, there may also be legislative requirements to comply with regarding incorporating energy and water-saving features into your water tank plans.

Deciding Which Type of Tank to Get

There are various options to choose from, all with different pros and cons and price points. You first need to decide if you want to go down the route of having an underground tank put in, or if you’ll add an aboveground one.

Those put in underground require excavation machinery, concreting, and significant labor costs, as well as costs for things like site surveys and approvals. This makes them a big financial commitment.

Aboveground tanks are more affordable but again, there are numerous types and budgets to decide between. When you go to buy water tanks for your property, you must decide what material you want them to be made of. 

Metal tanks are built from flat-rolled or corrugated metal that’s coated or galvanized. They usually have a plastic inner lining. Polyethylene tanks are good for people who live near the beach since the plastic doesn’t rust. They often have bladder storage made from PVC or geotextile or other synthetic materials.

Fiberglass tanks are also resistant to rust but are more expensive than plastic ones. They’re designed to withstand extreme temperatures.

Concrete tanks usually get installed for industrial and agricultural purposes, as they’re particularly hardy and won’t blow away, rust, burn, melt, or otherwise have issues. They’re more expensive and often larger than most homeowners require, though.

Before buying, consider the weather around your home. Think not just about how tanks will handle different conditions, but also, for instance, if the water inside them will become untenable if the temperature drops or heats up too much.


Deciding on the right sized tank for your needs is another key factor. Your requirements will come down to the size of your household, what you want to use the water for and when, and the space you have available on your land to house a tank. Let's discuss what size you need below. 

What Size Water Tank Do You Need?

Residential rainwater tanks are available with a wide range of capacities. Head down to Home Depot and pick up a rain barrel with a 55-gallon capacity, or look elsewhere to source storage tanks with a capacity exceeding 6,000 gallons.

200 - 300 gallon capacity tanks are well suited for modern suburban homes. That's enough water to take care of gardening and to keep some on hand for emergencies.

Of course, if you plan on using the water throughout the home, you will require a larger capacity tank. YourHome advises on approximate sizing based on use. We've converted their data to gallons below.

  • Gardening: 45 - 500 gallon capacity
  • Flushing toilets and gardening: 500 - 800 gallon capacity
  • Flushing toilets, washing clothes and gardening: 800 – 1,300 gallon capacity
  • Catering for a home's complete water supply: 1,300 – 5,000 gallon capacity

A Slim Line tank from Bushman Tanks USA with a 530-gallon capacity measures 78 inches high x 86 inches long by 25 inches wide.

This could be a significant profile if adding to a small home, so the size of a tank is worth considering beyond water capacity.

How Much Rainwater Can You Collect?

The answer to this goes beyond the size of your tank as you also need to consider the span of a roof and the average precipitation in your area.

Innovative Water Solutions reveals a simple formula for calculating the estimated collectable water from your home. Roof Area (ft2) x Precipitation Amount (in) x 0.623 = Estimated Collection (gallons)

So, multiply the area of your roof by the depth of rainfall using a rain gauge, then multiply this by 0.623, and you will have an approximate measurement of how much water can be harvested.

A more straightforward equation to remember is every inch of rain on a 1,000 square foot roof yields 623 gallons. You can get a good idea of expected rainfall by relying on the annual precipitation chart below.

Annual Precipitation Chart Used for Rainwater Harvesting

Source: Prism Climate Group

Using this data, we can estimate that homes on the east coast could expect to harvest over 25,000 gallons annually. In contrast, Montana, Nevada or Colorado should expect to obtain no more than 5,000 - 10,000 gallons of rainwater.

Is it Illegal to Use Rainwater Harvesting Systems?

It may surprise you to learn that many Americans believe that it's illegal to harvest rainwater. And yet, this is simply untrue. It's perfectly legal to harvest rainwater for personal use.

Certain states do have restrictions in place, which stipulate the quantity of water that can be harvested and its use.

The World Water Reserve reveals 12 states with restrictions on rainwater use: Arkansas, California, Colorado, Georgia, Illinois, Kansas, Nevada, North Carolina, Ohio, Oregon, Texas and Utah.

Most restrictions require citizens to register with local environmental departments before harvesting rainwater. However, several states are stricter.

Georgia, for example, only permits collected water to be used outdoors. Then in Colorado, residents are limited to a total of 110 gallons of rainwater collected across no more than two rain barrels. The rainwater collection can also only be used for gardening.

Utah has a 100-gallon cap on rainwater unless you register with the Division of Water Resources. Then you can harvest up to 2,500 gallons.

Most restrictions relate to the prior appropriation laws, which are still embedded in the culture of several western states.

Storage Tank Rebates

Many regions of the United States support rainwater harvesting and even offer financial incentives for equipping your home with a tank. These come in the form of rebates. These areas include Arizona, California, Iowa, Kansas, New Jersey, New Mexico, and Texas. 

For example, Santa Rosa, California residents are entitled to a rebate of $0.25 per gallon of approved rainwater storage. Purchase a 1000 gallon tank, and that's $250 returned to your pocket.

Head to the nation's capital, and Washington D.C. residents are entitled to $2 per gallon. So a 50-gallon barrel would entitle the user to a $100 rebate, which extends up to a maximum $1000.

Rebates are constantly changing, with many available for set timeframes. Before making a purchase, contact your local council or environmental department to see what rebates are currently available in your area.

Rainwater Tank Installation and Maintenance

Cleaning Gutters for Rainwater Harvesting

You can tackle rainwater tank installation as a DIY project unless residing in a state like Arkansas that requires a system to be designed by a professional engineer.

The best time to install a tank is before the wet season to maximize the collected rainwater. The tank should be positioned close to the house so the downpipe can be redirected to the tank.

The foundation needs to be levelled, and a reinforced concrete foundation or strong stand is required for large tanks.

A professional plumber should install accessories like first flush diverters and pumps to generate pressure who can then also connect the tank to your faucets for washing and flushing.

Rainwater tanks are built tough, so there's little maintenance required. Most work involves keeping the roof and gutters clean and treating the water intended for drinking.

To help you with this task, be sure to check our review on the best gutter cleaners on the market. 

Over the years, fittings like gutter guards, mosquito and rodent mesh may wither and need to be replaced. If living in a colder climate, there's a low risk of the tank freezing.

Insulating the tank's exterior with a thermal blanket or polystyrene can reduce the risk of freezing water. Round water tanks are also less likely to freeze than rectangular or square tanks as they have a smaller surface area.

The Future of Rainwater Harvesting

Did you know that Napa County requires new homes and those in rural locations to have a minimum of 2,500 gallons of water on hand for fighting fires?

So, stored water tanks are becoming a legal requirement, and this trend is expected to grow as we face increasing threats from global warming.

A growing focus on water conservation and sustainability could see water tanks become standard for all new homes and developments, and it's easy to see why.

Harvesting rainwater can help individuals and the community—the more people who explore rainwater tanks, the greater the benefits. 

About the Author Pat Moreno

Pat is our gardening tool expert here at Sumo Gardener. Working for many years as a private and commercial landscaper, Pat has used almost every type of gardening tool there is. Along with a vast knowledge for types of plants and putting together an amazing looking and maintainable garden, Pat developed a passion for gardening tools as he found that using the right tools vastly improved the ease and outcome of any landscaping job he undertook. When spending hours, days or years using a particular tool, you want to make sure you’ve got the best one for the job, and Pat is the right guy to guide us to the best gardening tools.

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