The knowledge about "civil engineering" provided by Er. Md Faiz Ali through this plateform is absolutely correct and verified based on practical knowledge and good experiences.


-:Water harvesting :-

Water harvesting means capturing rain water, where it falls and capture the runoff from, catchment and streams etc. Generally, water harvesting is direct rainwater collection. This collected water could be stored for later use and recharged into the ground water again.

Water Harvesting

It's illegal to collect rain water in some american states   


What is the requirement of water harvesting?

  • To arrest ground water decline and augment ground water table
  • To beneficiate water quality in aquifers
  • To conserve surface water runoff during monsoon
  • To reduce soil erosion
  • To inculcate a culture of water conservation

What is rain water?

Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then precipitated—that is, become heavy enough to fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth.

Roof top rain water harvesting

Rooftop Rain Water Harvesting is the technique through which rain water is captured from the roof catchments and stored in reservoirs. Harvested rain water can be stored in sub-surface ground water reservoir by adopting artificial recharge techniques to meet the household needs through storage in tanks..

Water harvesting methods

Water harvesting methods.

Methods of rain water harvesting

Rainwater harvesting is the collection and storage of rainwater for reuse on-site, rather than allowing it to run off. These stored waters are used for various purposes such as gardening, irrigation etc. Various methods of rainwater harvesting are described in this section.

There are two way of rain water harvesting.

  1. Surface runoff harvesting.
  2. Roof top rain water harvesting.

Surface runoff harvesting.

In urban area rainwater flows away as surface runoff. This runoff could be caught and used for recharging aquifers by adopting appropriate methods.

Roof top rain water harvesting.

It is a system of catching rainwater where it falls. In rooftop harvesting, the roof becomes the catchments, and the rainwater is collected from the roof of the house/building. It can either be stored in a tank or diverted to artificial recharge system. This method is less expensive and very effective and if implemented properly helps in augmenting the ground water level of the area.

Component of the roof top rain water harvesting.

The illustrative design of the basic components of roof top rainwater harvesting system.

(Component of rain water harvesting)                                          

The system mainly constitutes of following sub components.
  1. catchment.
  2. Gutters.
  3. Down pipe.
  4. Transportation.
  5. Storage tank.
  6. Collection sump.
  7. Pump unit
  8. First flush.
  9. Filtration.
  10. Recharge structure.


The surface that receives rainfall directly is the catchment of rainwater harvesting system. It may be terrace, courtyard, or paved or unpaved open ground. The terrace may be flat RCC/stone roof or sloping roof. Therefore the catchment is the area, which actually contributes rainwater to the harvesting system.


Rainwater from rooftop should be carried through down take water pipes or drains to storage/harvesting system. Water pipes should be UV resistant (ISI HDPE/PVC pipes) of required capacity. Water from sloping roofs could be caught through gutters and down take pipe. At terraces, mouth of the each drain should have wire mesh to restrict floating material.

First flush.

First flush is a device used to flush off the water received in first shower. The first shower of rains needs to be flushed-off to avoid contaminating storable/rechargeable water by the probable contaminants of the atmosphere and the catchment roof. It will also help in cleaning of silt and other material deposited on roof during dry seasons Provisions of first rain separator should be made at outlet of each drainpipe.


There is always some skepticism regarding Roof Top Rainwater Harvesting since doubts are raised that rainwater may contaminate groundwater. There is remote possibility of this fear coming true if proper filter mechanism is not adopted. Secondly all care must be taken to see that underground sewer drains are not punctured and no leakage is taking place in close vicinity. Filters are used fro treatment of water to effectively remove turbidity, colour and microorganisms. After first flushing of rainfall, water should pass through filters. A gravel, sand and ‘netlon’ mesh filter is designed and placed on top of these torage tank. This filter is very important in keeping the rainwater in the storage tank

clean. It removes silt, dust, leaves and other organic matter from entering the storage tank. The filter media should be cleaned daily after every rainfall event. Clogged filters prevent rainwater from easily entering the storage tank and the filter may overflow. The sand or gravel media should be taken out and washed before it is replaced in the filter.

First step filtration of  water 
As well as there are various type of filtration has to do for get pure water.
  1. Sand gravel filter.
  2. Charcoal filter.
  3. PVC-PIPE filter.
  4. Sponge filter.

Sand Gravel Filter.

These are commonly used filters, constructed by brick masonry and filleted by pebbles, gravel, and sand as shown in the figure. Each layer should be separated by wire mesh.

Charcoal filter.

Charcoal filter can be made in-situ or in a drum. Pebbles, gravel, sand and charcoal as shown in the figure should fill the drum or chamber. Each layer should be separated by wire mesh. Thin layer of charcoal is used to absorb odor if any.

Charcoal filtration         

PVC-PIPE Filtration.

This filter can be made by PVC pipe of 1 to 1.20 m length; Diameter of pipe depends on the area of roof. Six inches dia. pipe is enough for a 1500 Sq. Ft. roof and 8 inches dia. pipe should be used for roofs more then 1500 Sq. Ft. Pipe is divided into three compartments by wire mesh. Each component should be filled with gravel and sand alternatively as shown in the figure. A layer of charcoal could also be inserted between two layers. Both ends of filter should have reduce of required size to connect inlet and outlet. This filter could be placed horizontally or vertically in the system.

PVC-Pipe Filter

Sponge Filtration.

It is a simple filter made from PVC drum having a layer of sponge in the middle of drum. It is the easiest and cheapest form filter, suitable for residential units.

Method of roof top rain water harvesting.

  1. Storage of direct use.
  2. Recharging ground water aquifers.

  • Recharging of bore wells
  • Recharging of dug wells.
  • Recharge pits
  • Recharge Trenches
  • Soak ways or Recharge Shafts
  • Percolation Tanks

Storage of direct use.

In this method rain water collected from the roof of the building is diverted to a storage tank. The storage tank has to be designed according to the water requirements, rainfall and catchment availability. Each drainpipe should have mesh filter at mouth and first flush device followed by filtration system before connecting to the storage tank. It is advisable that each tank should have excess water over flow system.

Excess water could be diverted to recharge system. Water from storage tank can be used for secondary purposes such as washing and gardening etc. This is the most cost effective way of rainwater harvesting. The main advantage of collecting and using the rainwater during rainy season is not only to save water from conventional sources, but also to save energy incurred on transportation and distribution of water at the doorstep. This also conserves groundwater, if it is being extracted to meet the demand when rains are on.

A white coated storage tank on a platform

Recharging ground water aquifers.

Ground water aquifers can be recharged by various kinds of structures to ensure percolation of rainwater in the ground instead of draining away from the surface. Commonly used recharging methods are,

a)  Recharging of bore wells.

Rainwater collected from rooftop of the building is diverted through drainpipes to settlement or filtration tank. After settlement filtered water is diverted to bore wells to recharge deep aquifers. Abandoned bore wells can also be used for recharge.

Optimum capacity of settlement tank/filtration tank can be designed on the basis of area of catchement, intensity of rainfall and recharge rate. While recharging, entry of floating matter and silt should be restricted because it may clog the recharge structure. First one or two shower should be flushed out through rain separator to avoid contamination.

b)  Recharging of dug wells.

Dug well can be used as recharge structure. Rainwater from the rooftop is diverted to dug wells after passing it through filtration bed. Cleaning and desalting of dug well should be done regularly to enhance the recharge rate. The filtration method suggested for bore well recharging could be used.

Recharging of dug well

c)  Recharge pits.

Recharge pits are small pits of any shape rectangular, square or circular, contracted with brick or stone masonry wall with weep hole at regular intervals. Top of pit can be covered with perforated covers. Bottom of pit should be filled with filter media.

                          The capacity of the pit can be designed on the basis of catchment area, rainfall intensity and recharge rate of soil. Usually the dimensions of the pit may be of 1 to 2 m width and 2 to 3 m deep depending on the depth of previous strata. These pits are suitable for recharging of shallow aquifers, and small houses.

d)  Recharge Trenches.

Recharge trench in provided where upper impervious layer of  soil is shallow. It is a trench excavated on the ground and refilled with porous media like pebbles, boulder or brickbats. it is usually made for harvesting the surface runoff. Bore wells can also be provided inside the trench as recharge shafts to enhance percolation. The length of the trench is decided as per the amount of runoff expected. This method is suitable for small houses, playgrounds, parks and roadside drains. The recharge trench can be of size 0.50 to 1.0 m wide and 1.0 to 1.5 m deep.

e)  Soak ways or Recharge Shafts.

Soak away or recharge shafts are provided where upper layer of soil is alluvial or less previous. These are bored hole of 30 cm diameter. up to 10 to 15 m deep, depending on depth of  previous layer. Bore should be lined with slotted/perforated PVC/MS pipe to prevent collapse of the vertical sides. At the top of soak away required size sump is constructed to retain runoff before the filters through soak away. Sump should be filled with filter media.

Soak away or recharge shafts

f)  Percolation Tanks.

Percolation tanks are artificially created surface water bodies, submerging a land area with adequate permeability to facilitate sufficient percolation to recharge the ground water. These can be built in big campuses where land is available and topography is suitable.

Surface run-off and roof top water can be diverted to this tank. Water accumulating in the tank percolates in the solid to augment the ground water. The stored water can be used directly for gardening and raw use. Percolation tanks should be built in gardens, open spaces and roadside green belts of urban area.

-:Model designs for Rain Water Harvesting and Artificial Recharge:-

Model designs for Rain Water Harvesting and Artificial Recharge have been prepared, which can be used depending upon the  suitability of the terrain.
  • Hilly and Inter-mountainous area
  • Alluvial Area
  • Hard Rock Area

Design of Tank Bund: 

The tank bund, for all practical purposes, is a small-sized earthen dam and its design and construction should be carried out in accordance with the principles applicable to earthen dams.
The bunds of a percolation pond may be of three types, i.e.

Type A: Homogeneous embankment type.
Type B: Zoned Embankment Type.
Type C: Diaphragm Type. 

Tank bunds in India are mostly of Type A and  Type B are constructed with soils excavated from pits in the immediate vicinity of the bund and transported to the bund. The Common Types of Bunds of Percolation Ponds are shown below.

Homogeneous embankment type.

Homogeneous embankment

Zoned embankment type.

Diaphragm type.

Recharge Pits.

Recharge pits are normally excavated pits, which are sufficiently deep to penetrate the low permeability layers overlying the unconfined aquifers. They are similar to recharge basins in principle, with the only difference being that they are deeper and have restricted bottom area. In many such structures, most of the infiltration occurs laterally through the walls of the pit as inmost layered sedimentary or alluvial material the lateral hydraulic conductivity is considerably higher than the vertical hydraulic conductivity. Abandoned gravel quarry pits or brick kiln quarry pits in alluvial areas and abandoned quarries in basaltic area scan also be used as recharge pits wherever they are underlain by permeable horizons. Nalah trench is a special case of recharge pit dug across a stream bed. Ideal sites for such trenches are in fluent stretches of streams. 

Design Guidelines.

  1. The recharging capacity of the pit increase with its area of cross section. Hence, it is always advisable to construct as large a pit as possible.
  2. The permeability of the underlying strata should be ascertained through infiltration tests before taking up construction of recharge pits.
  3. The side slopes of recharge pits should be 2:1 as steep reduce clogging and sedimentation on the walls of the pits.
  4. Recharge pits may be used as ponds for storage and infiltration of water or they may be back filled with gravel sand filter material over a layer of cobbles/boulders at the bottom.Even when the pits are to be used as ponds, it is desirable to provide a thin layer of sand at the bottom to prevent the silt from clogging permeable strata.
  5. As in the case of water spreading technique, the source water being used for recharge should be as silt-free as possible.
  6. The bottom area of the open pits and the top sand layer of filter-packed pits may require periodic cleaning to ensure proper recharge .Recharge pits located in flood-prone areas and on stream beds are likely to be effective for short duration only due to heavy silting . Similarly pits by the sides of stream beds  are likely to be effective for longer periods.
  7. In hard rock area, stream bed section crossing weathered rocks or section along prominent lineaments or intersection of lineament  from ideal location for recharge pits.

Ground water recharge for urban aria.

In rural areas, rain water harvesting is taken up considering watershed as a unit. Surface spreading techniques are common since space for such systems is available in plenty and quantity of recharged water is also large. Following techniques may be adopted to save water going waste through slopes, rivers, rivulets and nalas.

                    In urban areas, rain water available from roof tops of buildings, paved and unpaved areas goes waste. This water can be recharged to aquifer and can be utilized gainfully at the time of need. The rain water harvesting system needs to be designed in a way that it does not occupy large space for collection and recharge system. A few techniques of roof top rain water harvesting in urban areas are described below.

Recharge Pit.

  1. In alluvial areas where permeable rocks are exposed on the land surface or are located at very shallow depth, rain water harvesting can be done through recharge pits.
  2. The technique is suitable for buildings having a roof area of 100 sq.m. These are constructed for recharging the shallow aquifers.
  3. Recharge Pits may be of any shape and size. They are generally constructed 1 to 2 m. wide and 2 to 3 m deep. The pits are filled with boulders (5-20 cm), gravels (5-10mm) and coarse sand (1.5- 2mm) in graded form. Boulders at the bottom, gravels in between and coarse sand at the top so that the silt content that will come with runoff water will be deposited on the top of the coarse sand layer and can easily be removed. For smaller roof area, pit may be filled with broken bricks/ cobbles.
  4. A mesh should be provided at the roof so that leaves or any other solid waste / debris is prevented from entering the pit. A desilting /collection chamber may also be provided at the ground to arrest the flow of finer particles to the recharge pit.
  5. The top layer of sand should be cleaned periodically to maintain the recharge rate.
  6. By-pass arrangement is to be provided before the collection chamber to reject the first showers.
Recharge pit

Recharge trench.

  1. Recharge trenches are suitable for buildings having roof area of 200-300 sq. m. and where permeable strata is available at shallow depths.
  2. Trench may be 0.5 to 1 m wide, 1 to 1.5m. deep and 10 to 20 m. long depending upon availability of water to be recharge.
  3. These are back filled with boulders (5-20cm), gravel (5-10 mm) and coarse sand (1.5-2 mm) in graded form – boulders at the bottom, gravel in between and coarse sand at the top so that the silt content that will come with runoff will be coarse sand at the top of the sand layer and can easily be removed.
  4. A mesh should be provided at the roof so that leaves or any other solid waste/debris is prevented from entering the trenches and a desilting/collection chamber may also be provided on ground to arrest the flow of finer particles to the trench.
  5. By-pass arrangement is to be provided before the collection chamber to reject the first showers.
  6. The top layer of sand should be cleaned periodically to maintain the recharge rate.
Recharge trench

Trench with recharge well.

  1. In areas where the surface soil is impervious and large quantities of roof water or surface runoff is available within a very short period of heavy rainfall, the use of trench/ pits is made to store the water in a filter media and subsequently recharge to ground water through specially constructed recharge wells.
  2. This techniques is ideally suited for area where permeable horizon is within 3m below ground level.
  3. Recharge well of 100-300 diameter is constructed to a depth of at least 3 to 5 m below the water level. Based on the lithology of the area, well assembly is designed with slotted pipe against the shallow and deeper aquifer.
  4. A lateral trench of 1.5 to 3m width and 10 to 30 m length, depending upon the availability of water is constructed with the recharge well in the centre.
  5. The number of recharge wells in the trench can be decided on the basis of water availability and local vertical permeability of the rocks.
  6. The trench is backfilled with boulders, gravels and coarse sand to act as a filter media for the recharge wells.
  7. If the aquifer is available at greater depth say more than 20 m, a shallow shaft of 2 to 5 m diameter and 3-5 metres deep may be constructed depending upon availability of runoff. Inside the shaft a recharge well of 100-300 mm dia is constructed for recharging the available water to the deeper aquifers. At the bottom of the shaft a filter media is provided to avoid choking of recharge well.


-:Field visiting for build water harvesting tank:-

we are investigating after excavation of ground which is behind engineering block in my college campus.

   Borrow pit

We select this region to make pit because this aria is approximate