System of water distribution

Water distribution systems are generally designed to adequately satisfy the water requirements for a combination of domestic commercial industrial and firefighting purpose.
The performance of a distribution system can be judged on the basis of the pressure available in the system for a specific rate of flow.
The distribution system consists of a network of pipes with necessary appurtenances for transporting water from the purification plant to the consumers tap.
A good distribution system should satisfy the following requirements
The system should be capable of supplying water at consumers tab at a reasonable pressure head
It should be capable of meeting the fire demand simultaneously
Which should maintain the degree of purity
It should be completely water tight
It should easy to operate and maintain
Water should be available even during the breakdown period
It should be so laid that during repairs it does not cause obstruction to traffic
The initial cost of the distribution should be as low as possible

Methods of distribution
Independence upon the topography of the area
Gravity system
Pumping system
Combined gravity and pumping system

In the gravity system the source of water which show located with respect to the area of distribution that water is available with sufficient pressure at various points of the area and no pumping is required

In the pumping system water is pumped directly into the distribution system to achieve the required pressure. Such system is not desirable

Combined gravity and pumping system is the most common system adopted in most of the cases. The water purification works are located almost at the same level as the area of the distribution. In order to obtain sufficient distribution pressure filtered water is pumped into Clear Water Reservoir located either on a higher ground or elevated tower,

Pressure in the distribution main
Adequate pressure should be available in the distribution main at all points located even at the remote places. Leaders and pressure depends on the following things
The height to which water is required to be supplied
Fire fighting requirements
Whether the supply is metered or not
Availability of funds.

Minimum velocity of 0.6 metre per second should be maintained
The manual on water supply and treatment prepared by the Ministry of Urban Development gives following the recommendation for minimum residual pressure
For single storey buildings 7 metre
For two storey buildings 12 metre
For 3 storey building 17 metre
Distribution system should not ordinarily be designed for residual pressure exceeding 22 metres

Minimum pipe size
For population upto 50000….. 100 millimetres
For population above 50000…. 150 millimetres

Systems of water supply
Continuous system
Intermittent system

In continuous system water is available to the consumer for all the 24 hours a day
In intermittent system the water is supplied to the consumer only during some Fixed time of the day

Limitations of intermittent system
Non availability of water during the fire demand
Unnecessary domestic storage
Pollution of water
Size of pipes a are higher
Wastage from the common water taps
Higher staff requirement

Storage and distribution reservoirs
Storage and distribution reservoirs are important units in modern distribution system.
Water storage Reservires are required to store the treated water.
Distribution reservoirs provide service storage to meet the widely fluctuating demand of often imposed on a distribution system, Provide Storage for fire fighting and emergencies.
Mostly of elevated type. Serve the following purpose
They absorb the variations in demand
Reservoir make the pump to run at uniform rate
View results in overall reduction in the size of pumps files and treatment units, does make the distribution system economical.
They serve as Storage for emergencies such as outbreak of fire value of pumps are busting of Mains.
They maintain the desired pressure in the main constantly.

Types of storage and distribution reservoir
Surface reservoir
Elevated reservoir
Stand pipes

The storage capacity of the distribution Reservoir is based on following three requirements
Balancing or equalising release
Breakdown reserve
Fire reserve

Balancing or equalising storage can be calculated by using hydrograph method for mass curve method.
The breakdown storage is assumed as 25% of the total storage capacity
National Board of fire underwriters treatments that distributing Reservoir be made large enough to supply water for fighting a serious configuration for 10 hours in communities for more than 6000 people.