Water Supply Flashcards
What Locations can water be obtained from
Groundwater (aquifers), Surface water (Lakes and Rivers) and the Sea
Why are wells and Boreholes usually used for private water supply
They collect a very limited amount of water
Where is water disposed after it is treated in a sewage plant
Into Rivers, lake, sea or reused for landscaping, irrigation or industrial use.
How much water does an average domestic house use per person every day
About 150 litres
Why are reservoirs located in the places that they are
So that they can have a sufficient hydraulic head to drive water to the top of the highest buildings in the distribution network
What does hydraulic head mean
Liquid pressure
What is the minimum and maximum hydraulic he in a distribution main and why are they these values
Minimum - 30m for fire-fighting Purposes
Maximum - 70m as any more will put the network under too much pressure: forcing water out of joints and causing structural collapse of older elements of the network. Also can cause excessive noise
Why are pressure reducing Valves or individual storage tanks used in houses and flats
Most Modern domestic appliances are designed to operate at significantly less than a 30m pressure head
What is a solution to sourcing water to houses in flat locations
Using water towers
What is a solution to sourcing water to houses in excessively hilly locations
Having a system of staggered service reservoirs resulting in acceptable pressure loads
Where are water service pipes installed into houses
They are typically installed underground into the foundation and ground floor slab. Pipe sleeves are used to allow for flexible service piped to be installed when the fabric is complete. A 750mm gap is commonly used between the ground level and lower level of the service pipe
Why is a ring mains preferred for the installation in houses
It helps to avoid stagnant water and, as the water can flow both ways around the loop allows repairs to an isolate section of pipework without needing to shutdown the whole system
What loads can a water pipe experience during service
Static Pressure, Water Hammer and bending stresses. The pipe will also be subject to corrosive stresses, depending on the type of water and the nature of the ground.
What is the diameter of a service pipe
13mm
Why should mains pipes have a minimum depth of 750mm and a maximum depth of 1350mm
To protect the pipes from the elements and minimise ground movement damage
Why does reservoir water need to be treated before it can be used
Storage in reservoirs allows sedimentation of particulate matter
How is water treatment typically achieved
By injecting Chlorine and filtering the Water with sand
What Mineral salts are considered in the evaluation of water hardness
Calcium and Magnesium as they have soap destroying properties
What is temporary hardness of Water
When water has the presence of calcium carbonate, calcium bicarbonate and magnesium bicarbonate which dissolve into water as they pass through chalky soil. These salts are deposited as scale on heat transfer during boiling.
What is permanent hardness in water
When water has a presence of non-carbonate salts, for instance calcium sulphate, calcium chloride and calcium chloride. These have to be removed from the water chemically.
What does water pass through in water treatment to reduce hardness and scale from water
Zeolite Chemicals
How are chemical beds in the treatment with zeolite chemicals restored when beds are exhausted
They are back-flushed with brine to regenerate the zeolites
