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RAINWATER HARVESTING
Kaigangio
#1 Posted : Monday, October 05, 2009 9:12:00 AM
Rank: Elder


Joined: 2/27/2007
Posts: 2,768
Hi all,

With the portable drinking water becoming more and more scarce the world over,not much attention has been paid to the so called 'Rainwater Harvesting' which has a potential to provide more than 60% of the total water demand especially in our country Kenya. Below is an article by a hydrologist on the theory behind the Rainwater Harvesting that i thought was worth sharing and may help to understand why the government should make it mandatory for commercial and residential developers to do rainwater harvesting and why on an individual level should be a first priority to consider when building our dream homes...

What is rainwater harvesting?
Rainwater harvesting is a technology used to collect,convey and store rain for later use from relatively clean surfaces such as a roof,land surface or rock catchment. The water is generally stored in a rainwater tank or directed to recharge groundwater or dams (in large scale harvesting). Rainwater infiltration is another aspect of rainwater harvesting playing an important role in stormwater management and in the replenishment of the groundwater levels.
Rainwater harvesting has been practiced for over 4,000 years throughout the world,traditionally in arid and semi-arid areas,and has provided drinking water,domestic water and water for livestock and small irrigation. Today,rainwater harvesting has gained much on significance as a modern,water-saving and simple technology.
The practice of collecting rainwater from rainfall events can be classified into two broad categories: land-based and roof-based. Land-based rainwater harvesting occurs when runoff from land surfaces is collected in furrow dikes,ponds,tanks and reservoirs. Roof-based rainwater harvesting refers to collecting rainwater runoff from roof surfaces which usually provides a much cleaner source of water that can be also used for drinking.
Rooftop rainwater harvesting at the household level is most commonly used for domestic purposes. It is popular as a household option as the water source is close to people and thus requires a minimum of energy to collect it. An added advantage is that users own,maintain and control their system without the need to rely on other community members.
Why rainwater harvesting?
In many regions of the world,clean drinking water is not always available and this is only possible with tremendous investment costs and expenditure. Rainwater is a free source and relatively clean and with proper treatment it can be even used as a potable water source. Rainwater harvesting saves high-quality drinking water sources and relieves the pressure on sewers and the environment by mitigating floods,soil erosions and replenishing groundwater levels. In addition,rainwater harvesting reduces the potable water consumption and consequently,the volume of generated wastewater.
Application areas
Rainwater harvesting systems can be installed in both new and existing buildings and harvested rainwater used for different applications that do not require drinking water quality such as toilet flushing,garden watering,irrigation,cleaning and laundry washing. Harvested rainwater is also used in many parts of the world as a drinking water source. As rainwater is very soft there is also less consumption of washing detergent and cleaning powder. With rainwater harvesting,the savings in potable water could amount up to 50% of the total household consumption.
Criteria for selection of rainwater harvesting technologies
Several factors should be considered when selecting rainwater harvesting systems for domestic and irrigation uses as they are completely different. Some critical data has to be obtained from the local meteorological and water departments in order to arrive at the most appropriate method of harvesting.
Components of a rooftop rainwater harvesting system
Although rainwater can be harvested from many surfaces,rooftop harvesting systems are most commonly used as the quality of harvested rainwater is usually clean following proper installation and maintenance. The effective roof area and the material used in constructing the roof largely influence the efficiency of collection and the water quality.
Rainwater harvesting systems generally consist of four basic elements:
(1) a collection (catchment) area
(2) a conveyance system consisting of pipes and gutters
(3) a storage facility,and
(4) a delivery system consisting of a tap or pump.
Storage tanks or reservoirs
The storage reservoir is usually the most expensive part of the rainwater harvesting system such that a careful design and construction is needed. The reservoir must be constructed in such a way that it is durable and watertight and the collected water does not become contaminated.
All rainwater tank designs should include as a minimum requirement:
- a solid secure cover - a coarse inlet filter - an overflow pipe - a manhole,sump,and drain to facilitate cleaning - an extraction system that does not contaminate the water,e.g. a tap or pump.
Storage reservoirs for domestic rainwater harvesting are classified in two categories:
1. surface or above-ground tanks,most common for roof collection,and
2. sub-surface or underground tanks,common for ground catchment systems.
Materials and design for the walls of sub-surface tanks or cisterns must be able to resist the soil and soil water pressures from outside when the tank is empty. Tree roots can also damage the structure below ground.
The size of the storage tank needed for a particular application is mainly determined by the amount of water available for storage (a function of roof size and local average rainfall),the amount of water likely to be used (a function of occupancy and use purpose) and the projected length of time without rain (drought period).
Rainwater harvesting efficiency
The efficiency of rainwater harvesting depends on the materials used,design and construction,maintenance and the total amount of rainfall. A commonly used efficiency figure,runoff coefficient,which is the percentage of rainfall that appears as runoff,is 0.8 (80%).
Different roofing materials have different run-off coefficient or efficacies. For example if cement tiles are used as a roofing material,the year-round roof runoff coefficient is about one and a half times better than the clay tiles while plastic and metal sheets are the best.
For an effective operation of a rainwater harvesting system,a well designed and carefully constructed gutter system is also crucial. 90% or more of the rainwater collected on the roof will be drained to the storage tank if the gutter and down-pipe system is properly fitted and maintained. Common materials for gutters and down-pipes are metal and plastic,but also cement-based products,bamboo and wood can be used.
Designing a rainwater harvesting system
For the design of a rainwater harvesting system,rainfall data is required preferably for a period of at least 10 years. The more reliable and specific the data is for the location,the better the design will be. Data for a given area can be obtained at the meteorological departments,agricultural and hydrological research centres and airports. Once the relevant data has been obtained,the processing can then generate the storage tank volumes and sizes.
Benefits of rainwater harvesting
Rainwater harvesting in urban and rural areas offers several benefits including provision of supplemental water,increasing soil moisture levels for urban greenery,increasing the groundwater table via artificial recharge,mitigating urban flooding and improving the quality of groundwater. In homes and buildings,collected rainwater can be used for irrigation,toilet flushing and laundry. With proper filtration and treatment,harvested rainwater can also be used for showering,bathing,or drinking. The major benefits of rainwater harvesting are summarised below:
• rainwater is a relatively clean and free source of water
• rainwater harvesting provides a source of water at the point where it is needed
• it is owner-operated and managed
• it is socially acceptable and environmentally responsible
• it promotes self-sufficiency and conserves water resources
• rainwater is friendly to landscape plants and gardens
• it reduces stormwater runoff and non-point source pollution
• it uses simple,flexible technologies that are easy to maintain
• offers potential cost savings especially with rising water costs
• provides safe water for human consumption after proper treatment
• low running costs
• construction,operation and maintenance are not labour-intensive.
Disadvantages
The main disadvantages of rainwater harvesting technologies are the limited supply and uncertainty of rainfall. Rainwater is not a reliable water source in times of dry periods or prolonged drought. Other disadvantages include:
• low storage capacity which will limit rainwater harvesting,whereas,increasing the storage capacity will add to the construction and operating costs making the technology less economically feasible
• possible contamination of the rainwater with animal wastes and organic matter which may result in health risks if rainwater is not treated prior to consumption as a drinking water source
• leakage from cisterns can cause the deterioration of load-bearing slopes
• cisterns and storage tanks can be unsafe for small children if proper access protection is not provided.
Drinking water from rainwater
In many countries of the world where water resources are not available at a sufficient quality fit for human consumption,rainwater acts as a substitute for drinking water and other domestic uses. In some remote islands around the globe,rainwater may even act as the major potable water source for their population.

The most important issue in collecting rainwater is keeping it free of dirt such as leaves,bird droppings and dead animals,and avoiding contamination with pollutants like heavy metals and dust.

Rainwater can also be treated for use as a potable water source. The use of slow sand filtration has proved to be a simple and effective treatment technology for the elimination of most of the organic and inorganic pollutants that may be present in rainwater,as well as producing a virtually pathogen-free water for drinking.


NEVER TALK OF A RHINO IF THERE IS NO TREE NEAREBY - ZULU PROVERB
...besides, the presence of a safe alone does not signify that there is money inside...
mukiha
#2 Posted : Monday, October 05, 2009 9:25:00 AM
Rank: Elder


Joined: 6/27/2008
Posts: 4,114
@kaigangio;

That's quite a long story....didn't read all of it...I was intimidated by the length.

I guess what you are saying is that we should all harvest rain water and use it during the dry season.

In my shags,people have been doing that since time immemorial!! many have not even consumed half of their storage with the current dry spell.....

Behind the gardens...Behind the wall...Under the tree (Including: Red...Dark Blue...Yellow)
Nothing is real unless it can be named; nothing has value unless it can be sold; money is worthless unless you spend it.
Chaka
#3 Posted : Monday, October 05, 2009 9:44:00 AM
Rank: Elder


Joined: 2/16/2007
Posts: 2,114
@Kaigangio,

Long post ...I read it through and my eyes are paining.I hear in some places in Nairobi kanjo can arrest you for harvesting water.Gava should encourage this thing by removing VAT on roofing materials,pipes and water tanks(Not sure if VAT is charged on water tanks)
segemia
#4 Posted : Monday, October 05, 2009 10:08:00 AM
Rank: Member


Joined: 2/20/2009
Posts: 658
@ kaiganjo,

Thanks alot for the insight.

Under the 'Criteria for selection of rainwater harvesting technologies' subheading you are saying that there are several factors to be considered while selecting a rainwater harvesting system.

Which factors are these?


There are two types of people in the world...those who run the risks and those who always have the rope round their necks...
Kaigangio
#5 Posted : Monday, October 05, 2009 11:08:00 AM
Rank: Elder


Joined: 2/27/2007
Posts: 2,768
@ segemia,

some of the factors that i was talking about are:

1. type and size of catchment area

2. local rainfall data and weather patterns

3. family size

4. length of the drought period

5. alternative water sources

6. cost of the rainwater harvesting system.




NEVER TALK OF A RHINO IF THERE IS NO TREE NEAREBY - ZULU PROVERB
...besides, the presence of a safe alone does not signify that there is money inside...
Kaigangio
#6 Posted : Monday, October 05, 2009 11:17:00 AM
Rank: Elder


Joined: 2/27/2007
Posts: 2,768
@ chaka,

i have not heard of city council prohibiting the employment of rainwater harvesting technics in building rooves except from their water distribution network without a legal connection.

i dont think it will be much of an ado if instead of discharging the rain water from ones residence's roof through the drainage system into the storm water drains,one routes this water into a standby storage tank. at least this is not illegal.....


NEVER TALK OF A RHINO IF THERE IS NO TREE NEAREBY - ZULU PROVERB
...besides, the presence of a safe alone does not signify that there is money inside...
segemia
#7 Posted : Monday, October 05, 2009 11:51:00 AM
Rank: Member


Joined: 2/20/2009
Posts: 658
@ Kaiganjo

Thanks kaiganjo,but the factors you have indicated point towards rainwater harvesting for domestic use. I am also interested in the factors affecting the selection of a rainwater harvesting for Irrigation uses.


There are two types of people in the world...those who run the risks and those who always have the rope round their necks...
akowally
#8 Posted : Monday, October 05, 2009 11:59:00 AM
Rank: Veteran


Joined: 5/20/2008
Posts: 1,126
Location: Nairobi
also didn't get to read it all .... but harvestin is always a good idea

When we pray in praise to God,he makes a difference in our lives.
JOIN MY FREE MINI-COURSE FOR WRITERS. CLICK HERE
akowally
#9 Posted : Monday, October 05, 2009 12:00:00 PM
Rank: Veteran


Joined: 5/20/2008
Posts: 1,126
Location: Nairobi
also didn't get to read it all .... but harvestin is always a good idea

When we pray in praise to God,he makes a difference in our lives.
JOIN MY FREE MINI-COURSE FOR WRITERS. CLICK HERE
Baratang
#10 Posted : Tuesday, October 06, 2009 12:08:00 PM
Rank: Member


Joined: 10/6/2009
Posts: 587
Hello SK bloggers,

I have been a quiet background spectator since i was first introduced to this website which to say the least is a great site. The wealth of knowledge that I have acquired so far from here is very beneficial to me and my people at home. I must thank you all for the contributions and the stockskenya management who manage this site.

@ Kaigangio,

I have read your article keenly and it has attracted my attention in a way that you can never imagine. I live in a country which receives less than 200mm of rainfall per year and sometimes we stay for 2 to 3 years without receiving even a drop of rain. The rainwater harvesting has therefore been embraced by both hands by our government to tap the water from the little rains which we receive from time to time. This process is our livelyhood without which we are dead meat as the people's and the livestock's existence depends on the 'saved' water. This is also the reason why our government's policy on water management is very strict and always given the first priority.

I am particularly interested in the irrigation water harvesting which seems to have been a challenge in our country due to the unreliable low rainfall which is only available between october and december. I would like to gather more information on various possibilities or options available to make this irrigation water harvesting succeed in our community. Our government is fully supportive of citizens whose energies are directed towards agriculture activities.

Thank you.


From Nothing,Nothing can be Processed into Nothing.
Kaigangio
#11 Posted : Tuesday, October 06, 2009 4:32:00 PM
Rank: Elder


Joined: 2/27/2007
Posts: 2,768
@ segemia,

some of the factors affecting the selection of rainwater harvesting method for irrigation purposes are:

1. rainfall amounts,intensities,and evapo-transpiration rates

2. soil infiltration rate,water holding capacity,fertility and depth of soil

3. crop characteristics such as water requirement and length of growing period

4. hydrogeology of the site

5. socio-economic factors such as population density,labour,costs of materials and regulations governing water resources use.




NEVER TALK OF A RHINO IF THERE IS NO TREE NEAREBY - ZULU PROVERB
...besides, the presence of a safe alone does not signify that there is money inside...
Kaigangio
#12 Posted : Wednesday, October 07, 2009 3:53:00 PM
Rank: Elder


Joined: 2/27/2007
Posts: 2,768
@ baratang,

if i understood you correctly,you want to know the process of design or construction of a water storage reservoir and the type of reservoirs in use or that are used...right?

by the way which country do you come from?


NEVER TALK OF A RHINO IF THERE IS NO TREE NEAREBY - ZULU PROVERB
...besides, the presence of a safe alone does not signify that there is money inside...
amorphous
#13 Posted : Saturday, January 09, 2021 4:26:11 PM
Rank: Member


Joined: 5/15/2019
Posts: 664
Location: planet earth
Kaigangio wrote:
Hi all,

With the portable drinking water becoming more and more scarce the world over,not much attention has been paid to the so called 'Rainwater Harvesting' which has a potential to provide more than 60% of the total water demand especially in our country Kenya. Below is an article by a hydrologist on the theory behind the Rainwater Harvesting that i thought was worth sharing and may help to understand why the government should make it mandatory for commercial and residential developers to do rainwater harvesting and why on an individual level should be a first priority to consider when building our dream homes...

What is rainwater harvesting?
Rainwater harvesting is a technology used to collect,convey and store rain for later use from relatively clean surfaces such as a roof,land surface or rock catchment. The water is generally stored in a rainwater tank or directed to recharge groundwater or dams (in large scale harvesting). Rainwater infiltration is another aspect of rainwater harvesting playing an important role in stormwater management and in the replenishment of the groundwater levels.
Rainwater harvesting has been practiced for over 4,000 years throughout the world,traditionally in arid and semi-arid areas,and has provided drinking water,domestic water and water for livestock and small irrigation. Today,rainwater harvesting has gained much on significance as a modern,water-saving and simple technology.
The practice of collecting rainwater from rainfall events can be classified into two broad categories: land-based and roof-based. Land-based rainwater harvesting occurs when runoff from land surfaces is collected in furrow dikes,ponds,tanks and reservoirs. Roof-based rainwater harvesting refers to collecting rainwater runoff from roof surfaces which usually provides a much cleaner source of water that can be also used for drinking.
Rooftop rainwater harvesting at the household level is most commonly used for domestic purposes. It is popular as a household option as the water source is close to people and thus requires a minimum of energy to collect it. An added advantage is that users own,maintain and control their system without the need to rely on other community members.
Why rainwater harvesting?
In many regions of the world,clean drinking water is not always available and this is only possible with tremendous investment costs and expenditure. Rainwater is a free source and relatively clean and with proper treatment it can be even used as a potable water source. Rainwater harvesting saves high-quality drinking water sources and relieves the pressure on sewers and the environment by mitigating floods,soil erosions and replenishing groundwater levels. In addition,rainwater harvesting reduces the potable water consumption and consequently,the volume of generated wastewater.
Application areas
Rainwater harvesting systems can be installed in both new and existing buildings and harvested rainwater used for different applications that do not require drinking water quality such as toilet flushing,garden watering,irrigation,cleaning and laundry washing. Harvested rainwater is also used in many parts of the world as a drinking water source. As rainwater is very soft there is also less consumption of washing detergent and cleaning powder. With rainwater harvesting,the savings in potable water could amount up to 50% of the total household consumption.
Criteria for selection of rainwater harvesting technologies
Several factors should be considered when selecting rainwater harvesting systems for domestic and irrigation uses as they are completely different. Some critical data has to be obtained from the local meteorological and water departments in order to arrive at the most appropriate method of harvesting.
Components of a rooftop rainwater harvesting system
Although rainwater can be harvested from many surfaces,rooftop harvesting systems are most commonly used as the quality of harvested rainwater is usually clean following proper installation and maintenance. The effective roof area and the material used in constructing the roof largely influence the efficiency of collection and the water quality.
Rainwater harvesting systems generally consist of four basic elements:
(1) a collection (catchment) area
(2) a conveyance system consisting of pipes and gutters
(3) a storage facility,and
(4) a delivery system consisting of a tap or pump.
Storage tanks or reservoirs
The storage reservoir is usually the most expensive part of the rainwater harvesting system such that a careful design and construction is needed. The reservoir must be constructed in such a way that it is durable and watertight and the collected water does not become contaminated.
All rainwater tank designs should include as a minimum requirement:
- a solid secure cover - a coarse inlet filter - an overflow pipe - a manhole,sump,and drain to facilitate cleaning - an extraction system that does not contaminate the water,e.g. a tap or pump.
Storage reservoirs for domestic rainwater harvesting are classified in two categories:
1. surface or above-ground tanks,most common for roof collection,and
2. sub-surface or underground tanks,common for ground catchment systems.
Materials and design for the walls of sub-surface tanks or cisterns must be able to resist the soil and soil water pressures from outside when the tank is empty. Tree roots can also damage the structure below ground.
The size of the storage tank needed for a particular application is mainly determined by the amount of water available for storage (a function of roof size and local average rainfall),the amount of water likely to be used (a function of occupancy and use purpose) and the projected length of time without rain (drought period).
Rainwater harvesting efficiency
The efficiency of rainwater harvesting depends on the materials used,design and construction,maintenance and the total amount of rainfall. A commonly used efficiency figure,runoff coefficient,which is the percentage of rainfall that appears as runoff,is 0.8 (80%).
Different roofing materials have different run-off coefficient or efficacies. For example if cement tiles are used as a roofing material,the year-round roof runoff coefficient is about one and a half times better than the clay tiles while plastic and metal sheets are the best.
For an effective operation of a rainwater harvesting system,a well designed and carefully constructed gutter system is also crucial. 90% or more of the rainwater collected on the roof will be drained to the storage tank if the gutter and down-pipe system is properly fitted and maintained. Common materials for gutters and down-pipes are metal and plastic,but also cement-based products,bamboo and wood can be used.
Designing a rainwater harvesting system
For the design of a rainwater harvesting system,rainfall data is required preferably for a period of at least 10 years. The more reliable and specific the data is for the location,the better the design will be. Data for a given area can be obtained at the meteorological departments,agricultural and hydrological research centres and airports. Once the relevant data has been obtained,the processing can then generate the storage tank volumes and sizes.
Benefits of rainwater harvesting
Rainwater harvesting in urban and rural areas offers several benefits including provision of supplemental water,increasing soil moisture levels for urban greenery,increasing the groundwater table via artificial recharge,mitigating urban flooding and improving the quality of groundwater. In homes and buildings,collected rainwater can be used for irrigation,toilet flushing and laundry. With proper filtration and treatment,harvested rainwater can also be used for showering,bathing,or drinking. The major benefits of rainwater harvesting are summarised below:
• rainwater is a relatively clean and free source of water
• rainwater harvesting provides a source of water at the point where it is needed
• it is owner-operated and managed
• it is socially acceptable and environmentally responsible
• it promotes self-sufficiency and conserves water resources
• rainwater is friendly to landscape plants and gardens
• it reduces stormwater runoff and non-point source pollution
• it uses simple,flexible technologies that are easy to maintain
• offers potential cost savings especially with rising water costs
• provides safe water for human consumption after proper treatment
• low running costs
• construction,operation and maintenance are not labour-intensive.
Disadvantages
The main disadvantages of rainwater harvesting technologies are the limited supply and uncertainty of rainfall. Rainwater is not a reliable water source in times of dry periods or prolonged drought. Other disadvantages include:
• low storage capacity which will limit rainwater harvesting,whereas,increasing the storage capacity will add to the construction and operating costs making the technology less economically feasible
• possible contamination of the rainwater with animal wastes and organic matter which may result in health risks if rainwater is not treated prior to consumption as a drinking water source
• leakage from cisterns can cause the deterioration of load-bearing slopes
• cisterns and storage tanks can be unsafe for small children if proper access protection is not provided.
Drinking water from rainwater
In many countries of the world where water resources are not available at a sufficient quality fit for human consumption,rainwater acts as a substitute for drinking water and other domestic uses. In some remote islands around the globe,rainwater may even act as the major potable water source for their population.

The most important issue in collecting rainwater is keeping it free of dirt such as leaves,bird droppings and dead animals,and avoiding contamination with pollutants like heavy metals and dust.

Rainwater can also be treated for use as a potable water source. The use of slow sand filtration has proved to be a simple and effective treatment technology for the elimination of most of the organic and inorganic pollutants that may be present in rainwater,as well as producing a virtually pathogen-free water for drinking.


NEVER TALK OF A RHINO IF THERE IS NO TREE NEAREBY - ZULU PROVERB



This is an excellent article. Enjoyed reading it. Asante!

I can definitely attest to the benefits of rain water harvesting from a clay tile roof. My frens, let me tell you, there is no better feeling than seeing God's rain falling all around us in DC, grabbing your umbrella, emerging from the hao and heading to inspect the underground water tank. The most glorious sound is the sound of the inlet pipe "crying" shwaaaaaaaaaaaaaaa as the water rolls into the tank from the four sections of the roof all connected by underground piping. That is a sound I could listen to for hours.

I am curious about this sand filter system. Can anyone find us a youtube video or two of this. I use my collected water for bathing, washing etc but I want to get it to potable level using a very low tech system. Water independence is a beautiful thing my brodas. Especially during these strange corona times!

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