Types of Water Demand in cities commercial areas #civilengineering @WATER AND WASTE WATER ENGINEERING

 

Types of Water Demand

As discussed earlier, the water consumption of the city is broken down into several categories, which is termed as types of water demand.

Primarily, six types of water demand are identified:

1. Domestic water demand
2. Industrial water demand
3. Institutional and commercial water demand
4. Demand for public uses
5. Fire demand
6. Water demand to compensate losses in waste and theft

1. Domestic Water Demand                             

The water required for domestic purposes in residential areas comes under domestic water demand. 50-60% of the water consumption (i.e. more than half!) is used under domestic water demand.

Domestic water demand includes water for:

• Drinking
• Cooking
• Bathing
• Lawn sprinkling
• Gardening
• Sanitary purposes

As per IS 1172-1993: Water required in above activities is estimated to be 200 lpcd minimum in a town having full flushing system. This water demand is lowered to 135 lpcd in economically weaker sections (EWS) and low income group (LIG).

The breakdown of annual average water demand is tabulated below for Indian towns and cities having flushing systems (200lpcd) and for low income sections (135 lpcd). The below tables are taken from IS 1172 – 1993.

Domestic Water Demand as per IS 1172 – 1993 in Towns/Cities (India)

Use	Water Consumption (Full Flushing System) in litre/capita/day	Water Consumption (EWS & LIG) in litre/capita/day
Drinking	5	5
Cooking	5	5
Bathing	75	55
Washing Clothes	25	20
Washing Utensils	15	10
Washing House Floors	15	10
Watering Lawns & Gardens	15	–
Flushing Water Closets	45	30
TOTAL	200 lpcd	135 lpcd

In Indian conditions, the IS code limits the daily water consumption to 225 lpcd. However, in developed and effluent countries like the USA, the water demand may be as high as 340 lpcd.

Domestic water demand increases with improvement in living conditions as rich lifestyle increases water consumption in:

• Air cooling
• Bathing under showers/bath-tubs
• Dish washing of utensils
• Car washing
• Home laundries
• Garbage grinders
• Gardening
• Water sprinkling in lawns

Total Domestic Water Demand

Total domestic water demand comes from 2 parameters:

1. Design population
2. Per capita domestic consumption of water

Total domestic water demand = total design population * daily domestic water consumption per head

2. Industrial Water Demand

Industrial water demand includes not only includes water demand of existing industries but also of the industries to be started in future.

Industrial water demand is normally taken 50 lpcd. But this industrial water demand may also be as high as 450 lpcd.

Industrial water demand depends on type and number of industries present in the city.

Industrial water demand may be estimated by considering:

• Nature of industry
• Size of industry
• Quantity of water required for unit production
• Future expansion potential of industry

There are some industries which develop their own water supplies. These industries play a very little to no role in public water demand.

Industrial Water Demand of Certain Industries

Sr No	Industry	Unit of Production Or Unit of Raw Material	Approx Water Requirement per Unit of Production/Raw Materials
1	Automobiles	Vehicle	40 kilolitre
2	Distillery (Alcohol)	kilolitre	122-170 kilolitre
3	Fertilizer	Tonne	80-200 kilolitre
4	Leather (tanned)	Tonne	40 kilolitre
5	Paper	Tonne	200-400 kilolitre
6	Special quality paper	Tonne	400-1000 kilolitre
7	Straw board	Tonne	75-100 kilolitre
8	Petroleum refinery	Tonne (Crude)	1-2 kilolitre
9	Steel	Tonne	200-250 kilolitre
10	Sugar	Tonne (Crushed cane)	1-2 kilolitre
11	Textile	Tonne (Goods)	80-140 kilolitre
Industrial water demand is being reduced with continuous modernization and water reuse

3. Institutional and Commercial Water Demand

Water requirement for trade and business purposes as well as institutions is included in this category like:

• Hospitals
• Schools and colleges
• Hotels and restaurants
• Railway stations
• Offices
• Factories

Institutional and commercial water demand depends upon:

• Nature of city
• Type of commercial establishments
• Number of commercial establishments
• Number of institutions present

In general, commercial and institutional water demand is taken as 20 lpcd. This number may rise to 50 lpcd in highly commercialized cities.

Commercial and Institutional Water Demand of some of institutions and commercial establishments are tabulated below:

SR NO	Type of Institution/Commercial Establishment	Average Water Demand
1	Offices	45-90 lpcd
2	Factories (bathrooms provided)	45-90 lpcd
3	Factories (bathrooms not provided)	30-60 lpcd
4	Schools Day scholars Residential	45-90 lpcd 135-225 lpcd
5	Hostels	135-180 lpcd
6	Hotels	180 litre/bed
7	Restaurants	70 litre/seat
8	Hospitals (including laundry) No. of bed ≤ 100No. of bed > 100	340 litre/bed 450 litre/bed
9	Nursing homes and medical quarters	135-225 lpcd
10	Cinemas, concert halls, theatres	15 litre/seat
11	Railway stations Junctions (mail & express train stop)Intermediate stations   Terminal railway stations	70 lpcd (with bath) 45 lpcd (without bath) 45 lpcd (with bath) 23 (without bath) 45 lpcd
12	Airports (international and domestic)	70 lpcd

4. Water Demand for Public or Civic Uses

Water required for public utility purposes are included in this category:

• Watering of public parks
• Gardening
• Road washing
• Use in public fountains
• Sanitation
• Public sanitary blocks cleaning
• Flushing sewer systems

Water provision for the above activities is tabulated below:

SR NO	Type of Public Usage	Civic Water Demand (Water Demand for Public Use)
1	Road washing	5 lpcd
2	Sanitation	3-5 lpcd
3	Parks & Gardens	2-3 l/m2/d

In India, for most of the public water supply schemes, water demand for public use is not considered a necessity. Most of the times a nominal amount of < 5% of total water demand is added arbitrarily for public use.

5. Fire Demand of Water

There is possibility of fire break out in thickly populated and industrial areas. If not controlled timely, serious loss is incurred.

To fight fire, fire fighting squads are maintained in developed cities. These fire fighting squads require huge amount of water to project the water at high speed over fire.

In modern public water supply schemes, provision for fire fighting is included. Also, fire hydrants are spaced 100-150 m in water mains to which fire fighting pumps can be connected immediately during fire. The pumps project water at high pressure exceeding 10-15 m of water head (100-150 kN/m²) for 4-5 hours.

The total water demand for fire fighting is small. But rate of water consumption when fire breaks out is very high. The minimum fire demand of water is taken as the amount and rate of water supply enough to extinguish the largest probable fire in the city.

Empirical Formula to Calculate Fire Demand of Water

1. Kuchling’s formula
2. Buston’s formula
3. Freeman’s formula
4. National board of fire underwriters formula

1. Kuchling’s Formula

2. Buston’s Formula

3. Freeman’s Formula

4. National Board of Fire Under Writers Formula

This calculation of fire demand is as per the recommendations of Board (now- American Insurance Association).

4 (a) For central congested high-valued city –

Population ≤ 2,00,000

Population > 2,00,000

Fire demand =

54600 litre/min + 9100-36400 litre/min (for second fire)

4 (b) For residential city –

1	Small/Low buildings	2200 lit/min
2	Larger/Higher buildings	4500 lit/min
3	High value residences, apartments, tenements	7650-13,500 lit/min
4	3-storeyed buildings	Up to 27,000 lit/min

While applying the above formulae excluding Kuchling’s formula, the total standby water allowance is

2-hours storage – Indian conditions (fairly good)

 5-10 hours storage – USA (minimum)

Limitation of Water Demand Formulae Discussed Above:

These formulae do not take into consideration the type of district served in fire fighting. The occurrence of fire is high in industrial areas as compared to residential areas.

The above limitation is eliminated in the following formula used in fire fighting in Jabalpur city, India:

For cities having population < 50 lakhs: Fire demand is ignored.

In moderate fire- 3 water jets are thrown at a time:

1. On burning property
2. Both  adjacent properties

Discharge in each water stream = 1100 lit/min

Assume 6 fires break outs in a day in big city; each for 3 hours.

Then water requirement will be as follows:

Fire demand = 6 × no. of fires × discharge × time of each fire

6 × (3 × 1100) × (3 × 60)

= 35,64,000 lit/day

Water requirement per person = 3564000/5000000 < 1 lpcd

6. Water Required to Compensate Losses in Thefts and Wastes

The following types of water losses are included in this category:

• Water leakage
• Leakage & overflow from service reservoirs
• Leakage from main & service pipe connections
• Leakage in consumer premises
• Large leakage from public taps
• Stolen water (unauthorized connections)

Careful maintenance and universal metering can reduce these losses. However, these losses are to be considered in water supply schemes.

These losses may be as high as 15% of total water requirement even when the water works are best managed. For unmetered water supply, the losses may even exceed up to 50%.

Summary

Water Demand: The total water required by the residents of city for different purposes is included in water demand.

Types of Water Demand:

1. Domestic Water Demand: The water required for domestic purposes like drinking, bathing, washing clothes and utensils, gardening, etc. is included in domestic water demand.
2. Industrial Water Demand: Depending upon the nature, type, size, and quantity of water required by unit production in industry, industrial water demand is estimated.
3. Institutional and Commercial Water Demand: Water required by various institutional and commercial establishments like hospitals, business hubs, offices, schools, hotels, restaurants, etc is included in this category.
4. Water Demand for Public or Civic Uses: Water required for public utility purposes like road washing, watering public parks, cleaning of public toilet blocks, etc. is included in this category.
5. Fire Demand of Water: To estimate the water required for fire fighting purposes, various empirical formulae are developed.
6. Water Required to Compensate Losses in Thefts and Wastes: Some allowance has to be made for the water loss due to leakage and stolen water.

Water Demand:

1	Domestic Water Demand	200 lpcd (135 minimum)
2	Industrial Water Demand	50 lpcd (rise up to 450 lpcd)
3	Institutional and Commercial Water Demand	45-450 lpcd
4	Water Demand for Public or Civic Uses	5 lpcd
5	Fire Demand of Water
6	Water Required to Compensate Losses in Thefts and Wastes	15-50 %