CHAPTER 3: C.
DESIGN PERIOD
WATER DEMAND
In commercial utility models, the design period
A. GENERAL normally spans long periods involving decades
The first step in designing a Level II or small Level within which the initial capital outlay and
III water system is to determine how much water is succeeding outlays for expansion and rehabilitation
needed by the population to be covered. The water can be rationally recovered. For small water
to be supplied should be sufficient to cover both the utilities, including those owned by the local
existing and future consumers. It must include governments, such large outlays are not available
provisions for domestic and other types of service and cannot be matched by the rural population’s
connections. capacity to pay. For these reasons, the design
period or horizon in this Manual is set at 5 or 10
Water demands are influenced by the following years.
factors:
1. Five – year design period
• Service levels to be implemented;
• Size of the community; • Advantages - Low initial capital cost. If the
• Standard of living of the populace; project is to be financed through a loan, the
• Quantity and quality of water available in loan amortizations are lower due to the
the area; lower investment cost.
• Water tariffs that need to be shouldered by • Disadvantages – Need for new capital
the consumers; outlays after five (5) years to upgrade
• Climatological conditions; system capacity. Most waterworks
• Habits and manners of water usage by the facilities, like reservoirs and pipelines are
people. more viable to plan for a one stage 10-year
period than to plan in two stages of 5-year
Once the consumption demands are defined, the period each.
next step is to determine the service level as part of
the demand analysis. 2. Ten-year design period
B. SERVICE LEVEL DEFINITIONS • Advantages – The water system facilities
are capable of meeting the demand over a
Level I (Point Source) - This level provides a longer period. No major investment cost is
protected well or a developed spring with an outlet, expected during the 10-year design period.
but without a distribution system. The users go to • Disadvantages – The higher initial capital
the source to fetch the water. cost will require initial tariffs to be set
higher.
Level II (Communal Faucet System or Stand
Posts) - This type of system is composed of a D. DESIGN POPULATION
source, a reservoir, a piped distribution network,
and communal faucets. Usually, one faucet serves The design population is the targeted number of
four to six households within a radius of 25 meters. people that the project will serve.
The consumers still go to the supply point
(communal faucet) to fetch the water. There are 2 ways of projecting the design
population.
Level III (Waterworks System or Individual House
Connects) – This system includes a source, a 1. Estimate the population that can be served by the
reservoir, a piped distribution network, and resources.
individual household taps. 2. Project the community or barangay population
and determine the potential service area4 and the
served population.
The historical population growth rates of the STEP 3. Projecting the Population Served
municipality/city/barangays are needed as the basis
for population projections. The population is Determining the actual potential users involves but
enumerated every 5 years (beginning on 1960, is not limited to the following activities:
except in 2005 where it was moved to 2007 due to
budgetary constraints). 1. Preparation of base maps;
2. Ocular inspection to gain familiarity with the
Steps 1-3 below are used to determine the design physical and socio-economic conditions of the
population: potential service area. Note that population
densities must be estimated;
STEP 1. Projecting Annual Municipal and 3. Delineation of the proposed service area (where
Barangay Growth Rates the pipes are to be laid);
4. Determination and assessment of the level of
The basic equations to be used to determine the acceptance by the residents of the planned water
average annual growth rate within the last censual system.
period (in this case from 2000 to 2007): 5. Assessment of the availability and
abundance/scarcity of alternative water sources,
such as private shallow wells, dug wells, surface
P2007 = P2000 (1 + GR)n waters, etc.
Or E. WATER CONSUMPTIONS
Water consumptions served by small water utilities
𝑷𝟐𝟎𝟎𝟕 𝟏 are commonly classified into Domestic Use,
𝑮𝑹 = ( )𝒏 − 𝟏 Commercial Use, Institutional Use, or Industrial
𝑷𝟐𝟎𝟎𝟎
Use. In rural areas, water consumption is generally
limited to domestic uses, i.e., drinking, cooking,
Where: cleaning, washing and bathing. Domestic
P2007 = population in 2007 consumption is further classified as either Level II
P2000 = population in 2000 consumption (public faucets) or Level III
GR = annual growth rate (multiply by 100 consumption (house connections)
to get percent growth rate)
n = number of years between the two 1. Unit Consumptions
census, in this case n = 7
Unit consumption for domestic water demand is
STEP 2. Projecting Municipal and Barangay expressed in per capita consumption per day. The
Populations commonly used unit is liters per capita per day
(lpcd). If no definitive data are available, the unit
Having projected the annual growth rates, the year- consumption assumptions recommended for Level
by-year population projections for the municipality II and Level III domestic usages in rural areas are
and barangays could then be computed by applying as follows:.
the basic equation
• Level II Public Faucets: 50 - 60 lpcd
Pn = P0 (1 + GR)n (Each public faucet should serve 4 - 6
Where:
households)
P = the projected population after nth year from
n
• Level III House Connections: 80 - 100 lpcd
initial year
P = the population in the initial year of the period
0
Concerned
GR = the average growth rate between the 2
periods
n = number of years between P0 and Pn
The unit consumptions of institutional and In actual operation, the NRW should be a cause of
commercial connections are, in terms of daily concern and should be subject to measures to keep
consumption per connection, usually expressed in it as low as possible. For planning purposes,
cubic meters per day (m3/d). however, a conservative approach should be
adopted. The water demand projection should
• Institutional Connections: 1.0 m3/d assume that the NRW of the new system will be
• Commercial Connections: 0.8 m3/d fifteen percent (15%) of the estimated
consumptions. The plan’s figure can be increased
2. Total Consumption up to a total of 20% at the end of 10 years. . These
assumed NRW figures require good maintenance
The total consumption is the sum of the domestic, of utilities, pro-active leakage prevention, and no
institutional, and commercial consumptions illegal connections for 100% recovery of supplied
expressed in m3/d. water.
a) Domestic Consumption G. WATER DEMAND
The year-by-year total domestic consumption is The water demand is a summation of all the
projected by applying the projected unit consumptions given in the preceding sections and
consumption to the projected population to be will determine the capacity needed from the
served for each year. source/s. The average daily water demand, also
known as the average day demand, is calculated
Based on experience, most water systems (in m3/day or lps) from the estimated water
originally constructed as Level II have upgraded consumptions and the allowance for the NRW
either to Level III or to a combined Level II and (expressed as a percentage).
Level III system.
A system with consumption of 2 lps with a 15%
In anticipation of the trend towards upgrading to NRW will have an average day demand equal to
Level III in the future, the Level II system planner
should assume that within 5 years, 90% of the 2 𝑙𝑝𝑠
= 2.4 𝑙𝑝𝑠
households served would opt for individual house (1 − 𝑁𝑅𝑊)
connections.
1. Demand Variations and Demand Factors
b) Institutional and Commercial Consumption
• Minimum day demand: The minimum
After having considered the possible timing and amount of water required in a single day
number of institutional and commercial over a year.
connections, the projected yearly consumptions for • Average day demand: The average of the
each category are estimated by applying the daily water requirement spread in a year.
corresponding projected unit consumptions as • Maximum day demand: The maximum
presented in the preceding amount of water required in a single day
section. over a year.
• Peak hour demand: The highest hourly
F. NON-REVENUE WATER (NRW) demand in a day.
Non-revenue water is the amount of water that is
produced but not billed as a result of leaks,
pilferages, free water, utility usages, etc. An
allowance should be made for this category;
otherwise, the designed source capacity would not
be sufficient to supply the required consumption of
paying customers.
2. Uses of the Demand Variations
• Minimum day demand: The pipe network
system is analyzed under a minimum
demand condition to check on possible
occurrence of excessive static pressures
that the system might not be able to
withstand. No point in the transmission and
distribution system should be subjected to
pressure more than 70 m.
• Average day demand: Annual estimates
and projections on production, revenues,
non-revenue water, power costs, and other
O&M costs are based on the average day
demand.
• Maximum day demand: The total
capacity of all existing and future water
sources should be capable of supplying at
least the projected maximum day demand at
any year during the design period.
• Peak hour demand: The pipeline network CHAPTER 4:
should be designed to operate with no point WATER SOURCES
in the system having pressure below 3
meters during peak hour conditions.
A. WATER RESOURCES
In the selection of a source or sources of water
supply, adequacy and reliability of the available
supply could be considered the overriding criteria.
Without these, the water supply system cannot be
considered viable. These, together with the other
factors that should be considered (and which are
interdependent), are as follows:
• Adequacy and Reliability
• Quality
• Cost
• Legality
• Politics
From the standpoint of reliability, the most
desirable supplies are, in descending order:
1. An inexhaustible supply, whether from surface
or groundwater, which flows by gravity through the
distribution system;
2. A gravity source supplemented by storage
reservoirs;
3. An inexhaustible source that requires pumping;
4. A source or sources that require both storage and
pumping.
B. BASIC CLIMATOLOGY OF THE C. CLASSIFICATION OF WATER SOURCES
PHILIPPINES
Water sources are generally classified according to
The Philippines has annual rainfall varying their relative location on the surface of the earth.
throughout the country from 965 mm (38 in) to These are characterized as follows:
4,064 mm (160 in). The monsoon rains are pulled
in by hurricanes or typhoons. The actual 1. Rainwater
distribution of rainfall varies widely with time and
location due to the archipelagic nature of the - Rainwater, or atmospheric water, is a
country’s geography and regional climatic product of water vapor that has risen
conditions. due to evaporation and accumulated in
the atmosphere, which condenses and
The tropical climate of the Philippines is marked falls on the Earth's surface.
by comparatively high temperature, high humidity,
and plenty of rainfall. The mean annual 2. Surface Water
temperature is 27.7° C. January is the coolest
month with a mean temperature of 22° C, while the - Surface water is exposed to the
warmest month is May with a mean temperature of atmosphere and subject to surface
34° C. runoff. It comes from rain, surface
runoff and groundwater, and includes
For purposes of understanding the available water rivers, lakes, streams, ponds,
sources for a distribution system, these are better impounding reservoirs, seas, and
characterized, based on the prevalent distribution oceans.
of rainfall, in classifications or types of climate
shown in Figure 4.1, and summarized as follows: 3. Groundwater
Type I: Two pronounced seasons: dry from - Groundwater is that portion of
November to April and wet during the rest of the rainwater which has percolated beneath
year. The western parts of Luzon, Mindoro, Negros the ground surface to form underground
and Palawan experience this climate. deposits called aquifers. The upper
surface of groundwater is the water
Type II: Characterized by the absence of a dry table.
season but with a very pronounced maximum rain
period from November to January. Regions with For rural water supply systems, groundwater is
this climate are located along or very near the generally preferred as a water source. The types
eastern coast. and extraction methods are as follows:
Type III: Seasons are not very pronounced but are Spring – is a point where groundwater flows out of
relatively dry from November to April and wet the ground and is thus where the aquifer surface
during the rest of the year. Areas under this type meets the ground surface. A spring may be
include the western part of Cagayan, Isabela, parts ephemeral (intermittent) or perennial (continuous).
of Northern Mindanao and most of Eastern
Palawan. Well – is a hole constructed by any method such as
digging, driving, boring, or drilling for the purpose
Type IV: Characterized by a more or less even of withdrawing water from underground aquifers.
distribution of rainfall throughout the year. Areas
with this climate include the Batanes group, Infiltration Galleries/Wells – Infiltration galleries
Northeastern Luzon, Southwest Camarines Norte, are horizontal wells, constructed by digging a
Western Camarines Sur, Albay, Northern Cebu, trench into the water-bearing sand and installing
Bohol and most of Central, Eastern and Southern perforated pipes in it.
Mindanao.
