HOW TO Harvest Rain Water

If you’re planning to move away from the city and start living off the grid, then harvesting rainwater is something you should seriously consider. It has a great potential to be your water source, and also it saves a lot of money on water expenses, as you can use it both indoors and outdoors. Harvesting rainwater can be done in the city and urban areas as well.

In this guide, we will share with you everything you need to know about rainwater harvesting, how it can be done, how to treat and clean the water and the different uses of the wate.

What is Rainwater Harvesting?

Rainwater harvesting is the process of collecting the runoff of the rain and then storing it for later use, both for indoor and outdoor needs. The most traditional way to harvest rainwater is by using the roof of the house. The rain collects in the gutters and then transfers the water to a storage device. This can be a barrel or other more advanced storage devices like a large tank, all of which we will elaborate later in the article.

Rainwater harvesting is becoming more and more popular all over the world. It’s an amazing alternative way for your household water supply and the uses of the water are diverse: it can be used for farming, cleaning the house, washing the car, and even for drinking and consumption after it’s treated properly. These are only a few uses of the water, as we will mention a little more down the road. In countries like Australia and Germany, where the green building movement is on the rise, rainwater harvesting is becoming a norm.

Harvesting rainwater means that you take control of the water supply and save a lot of money, and that you’re not dependent on urban infrastructure. The harvesting system can be designed and configured according to your needs and uses, both in the house and outdoors in the garden and landscape.

What Are the Benefits of Rainwater Harvesting?

We’ve already mentioned some of the benefits, but here is the complete list of all the benefits and advantages of collecting rainwater, storing it and then using it for various purposes. So, let’s list all the benefits, shall we?

  • Harvesting rainwater helps to conserve water.
  • You’re self-sufficient and don’t depend on anyone for your water supply (great for off-grid living or living in cities where there are restrictions on water use).
  • You save a lot of money on water expenses.
  • Rainwater is clean (relatively) and free.
  • Rainwater is not chlorinated which makes it better for plants and garden use.
  • You can use rainwater as your primary water source or treat it as a backup source for emergencies.
  • A big storm can leave behind a runoff that damages the ground. Collecting rainwater can take care of excessive runoff.
  • The technologies for rainwater harvesting are simple, inexpensive and easily maintained.
  • Not only do you enjoy free water, but it can also solve problems of drainage on your property.
  • The system can be built during construction of a new home or easily retrofitted to an existing home.
  • The system is extremely flexible which means that you can expand, reconfigure and even relocate it if needed.

What Can I Use Rainwater For?

Basically, anywhere tap water is used, so can rainwater be used, it’s as simple as that. Rainwater can be used for irrigation, indoors (without potable use) or for the entire house (including potable use). This is the big picture. Now, let’s get to specifics and see how exactly rainwater can be used inside and outside of the house:

  • Consumption/drinking (after properly treating and filtering the water)
  • Use it in toilets and for washing clothes
  • Washing the car
  • Watering your garden and lawn (by hand or by connecting the rainwater system to a sprinkler system/irrigation)
  • Refilling fish ponds and fountains
  • Refilling a swimming pool

What Are the Best Ways to Collect Rainwater?

In this section, we will list three methods which are used to collect rainwater. The difference between the systems is their scale, as in principle, they are all designed to do the same thing, and that is to collect the rainwater and store it. Now, let’s learn how to collect rainwater using barrel, the “dry” system and the “wet” system:

  • Collecting rainwater using barrels – This is the easiest and most common way to collect rainwater. All you need to do is install a barrel at the gutter downspout and collect the rainwater. This barrel can be new or recycled. The advantages of this system are that it can be implemented easily and by anyone, no matter where you live. You don’t need to spend a lot of money on installation of a large or complicated system. The barrels don’t use a lot of space. As for disadvantages, the rainwater you can collect is limited (50-200 litres), and it can easily overflow and thus waste water you could have collected.
  • The “dry” system – This system is similar to rainwater collection using a barrel, only here you use a much larger storage device. After each rain, the water collection pipe “dries” the rainwater from the roof directly into the storage device (from the roof and to the top of the tank). The advantages of this system are the ability to store a large amount of water. It is ideal in climates and areas where rainfall is infrequent and happens with large storm events. It’s not expensive to install the system, and because the system is not complicated, therefore it’s easily maintained. As for the primary disadvantage of this system, the storage device and tank must be located near the house.
  • The “wet” system – Using this system, the rainwater collection device or tank can be located away or farther from the house. Here, you install the pipes that collect the water underground to connect several or multiple downspouts from different gutters. The rainwater then fills the pipes underground, and then rises the vertical pipes to be transferred into the tank. Advantages of this system include the ability to collect rainwater from the entire surface and not just a specific spot of the roof. You can collect rainwater from multiple downspouts and gutters and you can also locate the big storage tank away from the house. The disadvantages are that this system is more expensive than the other systems, as you must install underground piping and maybe even apply pressure to lead the water into the tank (depending on the terrain and landscape). Also, gutters and tank inlets should differ from each other.

Water Storage Tanks

How Much Rainwater Can You Collect?

There’s actually a simple formula to help you calculate exactly the amount of rainwater that you can collect according to your living area and roof size.

The formula: annual average rainfall in your area x square meterage of your collection surface (roof) = total rainwater collection potential (litre).

Is It Safe to Drink Rainwater?

The rain that hits the roof and collection surface can wash with it various contaminants into the barrel or water tank. These contaminants may be bird poop or any other dirt that is present on the collection surface or the roof.

Even smoke and dust in the air can be dissolved in rainwater before it hits the roof. More than that, rainwater can carry with it viruses, bacteria, parasites and even chemicals that can lead to sickness and risk your health. Moving on, when the rainwater travels through the gutters, piping or even when it ends in the tank or barrel, the water can wash with it harmful chemicals like copper, lead and asbestos, not to mention dirt and germs.

Now, with all that said, it does not mean that you can’t use the rainwater for drinking. What you have to do is treat them properly, filter and purify them. Filtration removes debris from the water while purification or disinfection which is the next step, removes harmful substances and kills contaminants.

How to Filter and Disinfect Rainwater?

Today, many or almost all rainwater harvesting systems come with filtration tools and devices that are installed in the system. By using filters and screens, you’re not only ensuring that the water is cleaner, but also greatly reducing the need for maintenance of the system and allowing it to work for a longer period of time, with the piping and the entire system being cleaner.

Still, no matter how good the screens and filters are, particulates may find their way to the tank. So, in order to keep sediment at the bottom of the tank and not risk the rest of the water, you should always put the rainwater through screening, allow the sediment to settle without being disturbed, and also don’t use the water from near to the tank’s bottom. Instead you should place a floating filter, since it doesn’t disturb the sediment as it pulls the water from the tank’s middle.


Most of the systems use multiple filters. 

The first filters in a system are cartridge filters. Their rating is determined by the size of the tiniest particle they can filter. Smallest numbers correlate to better filtration. Keep in mind, though, that finer filters are also pricier and work slower. Remember to change the filters regularly. For wells as well as rainwater harvesting systems, you will need a larger (e.g., a 50 micron) filter or equivalent screen (e.g., 300 mesh). This is used in order to eliminate large particles as well as sand. It is best that this screen is accessed easily, as you’ll need to clean it every 3 months. Next you have another filter (20 or 10 micron filter), which is followed immediately by a 10 or 5 micron filter. You don’t have to clean these filters so often as the previous ones, so cleaning them once a year is enough.


In order to ensure that rainwater is safe for drinking, disinfection is a must, and that is the next step after filtration. In public water systems, disinfectants are added in order to destroy different microorganisms that may cause illness and disease both in people and animals. The same is required for rainwater.

Disinfection can be done using the following methods:


Chlorine has been disinfecting public water for centuries, eliminating waterborne diseases like cholera, dysentery, hepatitis and typhoid. The dosage rate will vary depending on the quantity, PH and temperature of the water that you want to disinfect and treat.

The downside of using chlorine to disinfect the water is that it might cause the appearance of such dangerous trihalomethanes (THMs) as the chloroform by simply combining with some natural organic material. Such a material can be a fulvic or humic acid, and these are frequently present in water. Because of that, it is crucial to keep the correct dosage rate when using this method. As for the smell and taste of the Chlorine, it can be removed using an activated carbon filter, also known as a charcoal filter. Filters with activated carbons are frequently produced from coconut shells, thus they are actually an ecologically green product.

Ultraviolet Light

For nearly 100 years, ultraviolet lights have been used in Europe. When using UV lights as the disinfection method, the water must pass first through filters. If you don’t use filters first, you risk bacteria and pathogens to cast shadows in the flowing water and basically, you allow different organisms to find their way to the water.

The way that the UV lights work is that it penetrates the cell walls of the organism and thus disrupts the genetic makeup of the cell. This makes it impossible for the organism to reproduce, leaving it harmless. The UV lights don’t damage or harm the water as it doesn’t change the chemical composition of the water and doesn’t leave any by-products as well.

In order for the process and the disinfection to be 100% effective, you must use the right dose of UV light to a specific unit of water. Also, the water must be clear of various particulates like suspended solids.

There are several things to remember when using a UV light:

  1. You should replace the bulb according to the manufacturer’s instructions (after 9,000 hours or approximately every year).
  2. Because UV light is not visible to the human eye, it may seem as if it is not lit, but in fact it is and so is working.
  3. You should occasionally clean the glass that encloses the light in order for the UV light to be effective.
  4. If you don’t install a backup light, then the water needs to be shut off upstream of the bulb before you replace the unit. It is recommended to shut down the system first and then disinfect the water downstream.
  5. Each UV unit comes with its own flow rate, and it absolutely must match the water’s flow rate.
  6. You should install the UV light unit after you’ve cleaned all the filters, resulting in clean water that is free of bugs and ready to use.

To make things simpler and more convenient, you can purchase a unit that cleans the bulb automatically. This will greatly reduce maintenance requirements.

Membrane Filtration

This method pushes water through a layer of material. Technologies of pressure-driven membrane include microfiltration, ultrafiltration, nanofiltration and reverse osmosis. It is able to remove pharmaceuticals and there are no byproducts left after the process is finished.

  1. Microfiltration (MF) – This is a membrane separation process that uses a pore size of .03 to 10 microns. The smaller the pore size, the more the system will remove. These membranes remove silt, sand, algae, clay, cysts and some bacteria.
  2. Ultrafiltration (UF) – In this method, the separation process is done by a pore size of approximately .002 to .1 microns. UF is able to remove anything that the MF system removes, and even some viruses.
  3. Nanofiltration membranes (NF) – These membranes have an approximate pore size of only .001 microns. Because the pore sizes are small, they require much more power in order to push water through the membrane. This causes more waste that is generated as opposed to the MF or UF systems. NF systems eliminate virtually all bacteria, viruses, cysts and other materials, including minerals.
  4. Reverse Osmosis (RO) – When talking about membrane technology, RO is the most widely used today. RO is able to remove particles as little as .001 microns, including natural organics, radium, cysts, bacteria, pesticides and viruses. It is recommended to look for a unit that is certified by NSF for contaminant reduction and not just safety. Also, you should know that these systems tend to produce waste water that has to be processed. The good news is that units that are newer are becoming “greener,” and thus produce less waste. The waste can be removed by including plumbing through a greywater system to the irrigation system or directly to the septic system. A whole-house unit can cost $8,000 or more (this depends on the size of your house and family/water usage). You should perform maintenance on a regular basis to ensure clean and safe water. The most important thing to do is to change cartridges.


This method separates the water from the impurities by heating and then collecting the condensation. Because the process is very intense, there is a loss of about 5%-10% of the water because of evaporation. Distillation can remove almost all substances from the water except for volatile organic chemicals (VOCs) that evaporate easily. Some distillation systems come with carbon filters that remove the VOCs.

The process of distillation is slow in order to reduce energy requirements and similar to RO systems, it stores the purified water in a tank for future use. Distillation systems use a lot of electricity and also generate heat. 

Tip: Before you invest money in filtration and/or purification equipment, invest in removing particulates before they find their way into the system. Install roof washers, gutter screens and leaf screens. Remember, it’s a lot easier to remove materials before they enter the system than dealing and removing them after they are already inside the system.

Water Filters

How to Maintain Rainwater Harvesting Systems

Because you’re the owner of the rainwater harvesting system, it is your responsibility to maintain it. Remember, that constant and correct maintenance won’t only ensure high quality water, but even prolong the system’s lifetime. When maintained properly, the rainwater is safe to be used both indoors and outdoors for all the uses we’ve mentioned earlier in this article.

We’ve talked about maintenance during the filtration and disinfection section, so here are a few tips:

  • Always clean and replace the filters and disinfection devices when required and according to the manufacturer’s instructions.
  • Regularly clean and inspect gutters and catchments to reduce the chance of contamination.
  • Do not mix water from other sources in the tank where you store the rainwater.
  • Clean the rooftop and catchment area just before heavy rain and thunderstorms arrive.
  • Cover the roof outlet on the terrace with a mesh. This will prevent leaves and other solid debris from entering the system.
  • Open the diversion valve for the first 5-10 minutes of rain in order to dispose of the first flush which is polluted. 

Final Words

There you have it, the most complete guide for rainwater harvesting. We hope we were able to clear every possible question and aspect of this endeavor. Harvesting rainwater can be an important part of your off grid life. It’s a unique and maybe somewhat challenging way to supply water to your household, but it’s worth every effort.