Water Supply Flashcards
Three waters integration
- strategic planning
- recognises inter-relationships
- integrates financial planning
Water Supply Sources
- groundwater bores
- reservoirs
- stream/river offtakes
- lakes
- de-salination
- roof water
- process water reuse
source determines level of treatment
what determines the level of treatment required
the source of the water
Water Supply Design Criteria
- water quality (must achieve minimum standard)
- hydraulic capacity (adequate for estimated use)
- structural strength of water system components to resist applied loads
- fire supply (must achieve standard)
- “fit for purpose” service life
- seismic resistance
- resistance to internal and external corrosion or degradation
- optimal “whole of life” cost for an asset life of 50 years
- capacity and ability to service future extensions and development
- networking, redundancy and security of supply
Water use breakdown inside NZ home
- 30% baths and showers
- 30% toilet flushing
- 20% kitchen use
- 20% laundry
Design Water Quantity
- between 180 and 250 litres per person per day, plus water used outside the house
- Summer can raise the average demand, inside plus outside, to 800 L/day
Non-residential water use
- commercial (cooling, bathrooms and landscaping)
- industrial (major uses for ‘process’ eg. rinse processes and sanitation)
- institutional (cooling, bathrooms and landscaping)
Industrial High Water Users
- food processing
- beverages
- textiles (due to dyeing/bleaching)
- semi-conductor manufacturing
- pulp and paper
Industrial Low Water Use
- warehouses
- electrical goods manufacture
Design Flow and Pressures
need to calculate:
- minimum water demand (e.g. 250 L/p/day)
- peak flow
- fire water demand
Network Design
- use models to assess combinations of pipe size, pressure and layouts
- ability to add future connections
- looping to provide flow security
- incorporate values for maintenance/fault isolation
- design pressures
- rate pipes for 1.5 times operating pressure
Pipe Materials
- ductile iron and steel
- PVC-U
- PE80, PE 100
Ductile Iron and Steel pipes
- internal lining and external coatings must be undamaged or fully restored after repairs or fabrication work
- potential problems with stray electric currents and bimetallic corrosion
PVC-U
- UV degradation
- scratching, gauging and impact damage
- proper bedding and installation required
- permeation by contaminants possible
PE 80 or PE 100
- susceptible to permeation by some hydrocarbon contaminants
- sophisticated equipment and highly skilled workers required
- UV degradation
- bedding support to prevent excessive deformation
- pulling forces for PE not to exceed manufacturer’s reccommendations
- minimum radii
- Poissons effect and end restraint
Typical fittings
- sluice valves
- backflow prevention
- scour valves
- air valves
- thrust and anchor blocks
- meters
Backflow
two basic causes:
- sudden drop in pipe pressure, causing water to siphon back into the system
- water supply directly connected to equipment, such as a boiler or a private bore, which is at higher pressure than the water supply system, forcing water into the supply system
backflow prevention design based on contamination risk
Construction considerations
- installation methods
- minimum cover
- backfill and bedding materials
- crossings (roads, railways, waterways)
- clearance to other services
- future access
- topographical and environmental considerations
Alternatives
small scale
- grey-water reuse
- rainwater tanks
when planning additional wells need to consider:
- how much water is needed
- target aquifer depth (yield and quality)
- interference effects on existing wells in the supply
- effects on other wells neighbouring the site
- any effects on streams
- potential for the source to be contaminated
Water Supply Risks
- climate effects
- abstraction effects
- water quality (diffuse and point source discharges)
