RAINWATER HARVESTING

Sagar Malsane, Asst. Prof., NICMAR

Introduction Elements of green building design

Building siting Building orientation Material selection Energy efficiency Water conservation Construction waste management Indoor air quality

Water SupplyGreater demand for water supply due to Inadequate harvesting Leakage in distribution systemMunicipal water supply system has 02 objectives Provide safe, potable water for domestic use. Water at sufficient pressure for fire protection.A typical waterworks consist of a Source treatment Pumping Distribution system

Introduction Rainwater falling on the building It falls on the roofs (catchment surface) Rainwater must be managed well Either disposed off or collected for use

Why dispose or harvest

Dampness and leakage inside the building due to rainwater ponding – unhygienic conditions

Rainwater Harvesting Gathering, or

accumulating and storing, of rainwater for the purpose of conservation

Rainwater HarvestingFeatures Rainwater falling on roof flows along

gutters Water flows through pipes to tank via filter Removing unwanted particles from

rainwater In-tank submersible pump delivers clean

rainwater to toilets, washing machine and outside tap

Rainwater Harvesting

Benefits

Saves money by reducing water usage

Helping to reduce flooding risks Gains Eco-homes rating points

for your property

Domestic wastewaterSanitary Sewer System

Domestic wastewaterStorm Sewer System

What decides the feasibility and necessity of RWH

Measurement of rainfall in a city

Intensity of rainfall

Corresponding building design

Measurement of rainfall in a city

Measured in mm or cm with rain gauge on monthly, annual basis

City Annual Rainfall, mm

Rainy Season % of total rainfall (rainy season)

Mumbai 2099 June - September 80

Kolkata 1751 June – September 75

Chennai 1215 August – November

67

New Delhi 712 July – August 55

Rain gauge

Intensity of rainfall Amount of rainfall in unit time, like per

hour Expressed in mm or cm/hour Rain gauge is used For building design purpose, min 20 – 25

years mean intensity data required

Rainwater IntensityCities Intensity (mm/hr)

Mumbai 125-130

New Delhi 70-80

Kolkata 70-80

Chennai 70-80

In the absence of the rainwater intensity data, empirical formula can be usedI = [F (T+1)]/T(t+1)

I = Intensity of rainfall, mm/hrF = Total rainfall in mm in time T (maximum intensity)T = Duration of storm, in hourst = Duration of storm intensity, hrs

Rainwater Harvesting Components Catchments: surface which directly

receives the rainfall. It can be a paved area like a terrace or courtyard of a building, or an unpaved area like a lawn or open ground, roof {(RCC), galvanised iron or corrugated sheets}

Coarse mesh at the roof to prevent the passage of debris

Rainwater Harvesting Components Gutters: 

Channels all around the edge of a sloping roof to collect and transport rainwater to the storage tank

The size of the gutter should be according to the flow during the highest intensity rain.

It is advisable to make them 10 to 15 per cent oversize.

Collection Eve’s gutter, piping system and storage

tank Commonly used 2 types of gutters – half

round and ogee

Gutter size

Size, mm Half round, ltrs/sec

Ogee, ltrs/sec

100 0.83 0.91

125 1.50 1.70

150 2.30 2.70

Rainwater Harvesting Components Conduits: pipelines or drains that carry

rainwater from the catchment or rooftop area to the harvesting system.

Piping system Must be approved by local authority Located in suitable part of a building Discharge directly into storm water

drainage system Cast iron, galvanised iron, PVC

Pipe diameter, how to decide

Pipe diameter, mm

Avg rate of rainfall, mm/hr

50mm 75mm 100mm

Average area, sq.m

50 13.40 8.60 6.60

65 24.10 16.00 12.00

Rainwater Harvesting Components First-flushing: device is a valve that

ensures that runoff from the first spell of rain is flushed out and does not enter the system.

Rainwater Harvesting Components Filter 

The filter is used to remove suspended pollutants from rainwater collected over roof(i) Charcoal water filterA simple charcoal filter can be made in a drum or an earthen pot. The filter is made of gravel, sand and charcoal, all of which are easily available.

Rainwater Harvesting Components (ii) Sand filters

Sand filters have commonly available sand as filter media.

Rainwater Harvesting Components Storage Tank

Purification Apertures

should be screened

Water passed through sand

First rain must be let go

Methods of harvesting Surface harvesting – dams, lakes, ponds, Underground harvesting – water

percolation in the ground – depends on rainwater intensity, rainfall, soil quality, vegetation, slope

Direct harvesting – water tank on ground Recharge well method – directly led to

the existing nearby well

Significance Rainwater harvesting provides an independent water supply during

regional water restrictions. Developed countries is often used to supplement the main supply. It provides water when there is a drought, prevents flooding of low-

lying areas, replenishes the ground water level, and enables dug wells and bore wells to yield in a sustained manner.

It also helps in the availability of clean water by reducing the salinity and the presence of iron salts.

Makes use of a natural resource and reduces flooding, storm water runoff, erosion, and contamination of surface water with pesticides, sediment, metals, and fertilizers.

Excellent source of water for landscape irrigation, with no chemicals such as fluoride and chlorine, and no dissolved salts and minerals from the soil.

Promotes both water and energy conservation. No filtration system required for landscape irrigation.

In the state of Tamil Nadu, rainwater harvesting was made compulsory for every building to avoid ground water depletion. It proved excellent results within five years, and every other state took it as role model. Since its implementation, Chennai saw a 50 percent rise in water level in five years and the water quality significantly improved.

At present, in Pune (in Maharashtra), rainwater harvesting is compulsory for any new society to be registered.

True water demand Bathing: 55 litres Toilet flushing: 30 litres Washing of clothes: 20 litres Washing the house: 10 litres Washing utensils: 10 litres Cooking: 5 litres Drinking: 5 litres.