Complete Guideline for Rainwater Harvesting

feature image - rainwater harvesting

Rainwater harvesting collects and uses rainwater from hard surfaces such as roofs to irrigate a landscape or flush toilets. A rainwater home harvesting system can be as simple as using a small homemade rain barrel or installing a large cistern or underground storage tank. 

Harvesting rainwater in your home or work reduces the amount of drinking water you would otherwise need for irrigation. It helps minimize runoff entering our combined sewer system during storm events.

Importance of Rainwater Harvesting

Ecologically there are four reasons why rainwater harvesting is essential for water conservation.

1. Preservation of Underground Water

The increasing demand for water increases groundwater extraction, thereby reducing underground water reserves. Rainwater harvesting systems are a helpful alternative.

2. Availability of Good Quality Water During Rainy Season

Water quality from water sources such as lakes, rivers, and underground water is very volatile. Collecting and storing rainwater can be a solution when surface water quality, such as a lake or river, becomes low during the rainy season, as is often the case in Bangladesh.

3. Creating Nearby water Resources

Other water sources are usually located far from the home or community of users. Collecting and storing water near the house will increase access to water supplies. It also positively impacts health and strengthens the user’s sense of ownership of this alternative water source.

4. Pollutant Free Water Resource

Water supplies can be polluted by industrial activities and human waste, such as entering minerals such as arsenic, salt, or fluoride. At the same time, the quality of rainwater, in general, is relatively good.

Cons of Harvesting Rainwater

Rainwater harvesting comes with some inconveniences of its own such as:

  1. Installing a relatively complex and expensive system is inevitable if one wants to use rainwater for all the household and sanitary tasks of the house.
  2. Unfortunately, with rainwater, we also recover the pollutants suspended in the air.
  3. The system is only functional above the freezing point. Therefore, it would be best to empty the tank in the fall to avoid breakage due to frost.
  4. A system to serve as a single water source for all families can be pretty expensive. 
  5. The collection water could be contaminated by leaching from roofing materials or mold and health risks.
  6. Unprotected stagnant water reserves can become a privileged nesting site for mosquitoes, vectors of diseases that threaten humans and animals.
Frozen Water tank in winter
Frozen Water tank in winter (source)

Uses of Rainwater

Not only is it worth collecting rainwater for the garden, but you can use it to your advantage around the house.

1. Toilet Flush

Since the water needed for the toilet does not have to be clean or filtered, you can use rainwater for this purpose.

2. Laundry

Since rainwater is free of limescale, it is much more suitable for washing clothes than most drinking water. If you wash with rainwater, you can do without fabric softener and save up to 60% detergent.

Uses of rainwater - Rainwater harvestting
Sketch representation of rainwater uses (source)

3. Irrigation water for indoor plants

Indoor plants are also happy with collected rainwater because they thrive best if you give them water containing little lime.

4. Drinking water

As for drinking water, it is not advisable to use the harvested rainwater for this purpose. If you want to utilize the harvested rainwater for drinking purposes, the water has to be treated first. 

Essential components of Rainwater harvesting System

Five essential components must be present in a rainwater harvesting system:

1. Collection module

The rainwater collection system begins through the collection module, responsible for collecting the water that falls. Generally, it is through the roof surface and the gutters placed around the constructions. Through this, the rainwater falls and runs off through these channels.

They should be kept clean to avoid contamination, and water gets filtered more easily. It is common for these gutters to have water residues and insects form because they are outside, so it is advisable to maintain them constantly.

2. Conduction module

In the collection module, the water is collected, but it cannot stay there stagnant but needs to move. It is precisely through the conduction module. It consists of a pipe that helps the water move from where it runs off to where it is to be stored.

The conduction module has a slope that helps it drain more straightforwardly since there would be water spillage without it. It is also advisable to check the pipeline to keep the water that falls as clean as possible.

3. Filtration system

This system is needed if you want to use harvested rainwater for drinking purposes. The water is led to a purification system, through which it reaches the place where it is to be stored.

Once it has gone through this purification process, it will be ready for human and domestic consumption. However, you don’t need this system if you use the harvested rainwater to wash clothes, dishes, do indoor and outdoor cleaning, and water the garden. 

essential components - water harvest
Setup for rainwater harvesting system (source)

4. Storage

In a rainy season, it is possible to catch high volumes of rainwater. Therefore, you should keep it in storage to ensure a supply for the season. So it would be best if you had a place to store rainwater in the form of barrels, tubs, or ponds. 

5. Distribution

The distribution system consists of a water pump to pump water from a reservoir or pond. So the harvested rainwater is ready to be used, just by turning on the faucet or where it will be deposited for the activity to be carried out.

WHO clean water standard guidelines for harvesting Rainwater

Constraints faced in harvesting rainwater include the fluctuating frequency and quantity of rain and the quality of rainwater that does not meet the WHO clean water standard guidelines

There are three issues related to rainwater quality: bacteriological water quality, the problem of insect vectors, and polluted water in the beginning phase of rain.

1. Bacteriological water quality

Rainwater can be contaminated by dirt in the roof, so it is advisable to keep the top clean. Rainwater reservoirs must also have a lid to avoid mud. Bacteria cannot live in clean water. 

Moss can live with sunlight through the water reservoir; therefore, the rainwater storage barrel should be dark and placed in the shade so that moss cannot grow.

2. Insect Vectors

Insects can reproduce by laying their eggs in water. Therefore, the water reservoir should be tightly closed to prevent the entry of insects such as mosquitoes. 

There are several simple treatment methods for using rainwater, including: 

  • Boiling water: to kill bacteria 
  • Adding chlorine: 35ml sodium hypochlorite per 1000 liters of water will disinfect the water 
  • Sand filtration ( bio-sand ) will remove harmful organisms. 
  • SODIS (Solar Water Disinfection) technique: a plastic bottle that has been painted black, filled with water, and dried for several hours to kill bacteria and microorganisms in rainwater
SODIS - rainwater harvesting
SODIS Methodaire (1) filling up the bottle (2) Providing solar heat (3) minimum 6 hours in the sun and (4) Pure drinkable water (source)

3. Disregard the Water from the first rains

They are the ones that will drag the pollutants present in the air and wash away the accumulated dirt in the catchment area. 

The technical recommendations by the United Nations Environment Programme (UNEP) indicate the disposal of around one to two liters of water from the first rain for each square meter of roof. Thus, if the top has 20 square meters, it is necessary to disregard a volume between 20 and 40 liters.

Rainwater collection at home

There are several ways to collect rainwater, some are simpler, and some are more expensive methods.

1. Easiest method

The simplest method to collect rainwater is to place a barrel or a rainwater collection tank under the gutter where rainwater flows from the roof.

It is elementary and one of the cheapest ways to collect rainwater. In addition, there is a wide variety of rainwater collection tanks that can be ornament for the garden.

Rainwater collecter - rainwater harvesting
Rainwater collecting kits 53-gallon capacity (Purchase Link)

But there are disadvantages to this solution. Such a tank will fill up quickly, and if excess water leaks out, it will drain off the house wall, damaging the wall structure.

The solution to this can be to tie several barrels in a row. Another disadvantage is that when the system is open, the water in the open becomes mosquito-infested.

Extracting water is not accessible from these tanks; they are best suited for filling rainwater into a watering can and sprinkling it that way. This process is aided by mounting a tap on the tank and placing it on a pedestal.

2. Overflow rainwater catchment

In this case, there is an overflow barrier between the gutter and the rainwater collection tank. When the barrels are full, excess water flows down the rain gutter.

3. The most professional method for rainwater harvesting

The most professional way to collect rainwater is to dig a rainwater collection tank into the ground. However, there’s quite a lot of work to do, and a large pit needs to be plowed into the garden so we can place the tank underground.

When it’s done, it doesn’t take up space and becomes invisible. To be able to use the collected rainwater, we will even need a pump.

4. Collect rainwater without a roof

If you want to collect rainwater without using roof and supply pipes, then the simple method to do so is by using tarpaulin.

  1. Stretch the tarpaulin
  2. Measure the height so that the stretched tarpaulin with the weight of the stone is above the ground
  3. Eyelets are connected with an anchor (fences, umbrellas, handles, wall hooks)
  4. Drive a hole in the middle of the tarp
  5. Put the stone
  6. Place the collection container under the perforated stone recess
  7. Now, the rain flowed by the tarp and channeled into the collection container through the hole. When it is not raining, leave the tarp to dry and store it in a box. 

Make rainwater drinkable

Rainwater contains various contaminants and should not be used for drinking without some treatment. We have listed four methods with which you can make rainwater drinkable.

1. Boiling 

Boiling water is a very safe method of making water drinkable in areas without filters or purifiers. However, to ensure that microorganisms have been eliminated, it is recommended to filter the water through a clean cloth and boil it for at least 5 minutes.

boiling water - rainwater harvesting
Pouring germs free boiling water (source)

2. Chlorination of Water

The chlorination of water is another possible mechanism to eliminate harmful microorganisms and thus make the collected rainwater drinkable. You can add chlorine according to the size of the container.

That is, for a liter of water, you must apply a drop of commercial chlorine, whose concentration is 5%. For 20 liters, use 20 drops of chlorine; for 200-liter water, add two chlorine caps, while for 1,000 liters, add ten chlorine caps. Then stir and wait 30 minutes to consume.

3. Solar Exposure

Place the water in a plastic container, and leave for 6 hours in the sun. This method is more suitable when the water is not visibly dirty.

4. Water Purifier

The water purifier is by far the best method to make the rainwater drinkable. It has a central filter element, a purification chamber with remarkable technologies, such as pumps or ultraviolet lamps, to eliminate bacteria.


Rainwater harvesting is one of the methods of water conservation that the community in the household can do. The UN has predicted by 2050, about 5 billion people won’t have access to clean water. So why not start harvesting rainwater now. 

If rainwater harvesting is practiced sustainably, it will help maintain water sustainability and environmental sustainability as a livelihood supporter for present and future generations.