Rain Water
South Australia is described anecdotally as the driest state
in the the driest continent on this planet.
That suggests that this land area is poorly resourced with naturally occurring water
sources; be they artesian (below ground), stationary or flowing
(ground level streams, dams, lakes) or airborne (rain).
Most streams in the region flow seasonally only, ground water
bodies are subject to high evaporation rates in summer, and
rain falls predominantly over a short winter season only.
In this situation, capture, retention and potability of
naturally occurring waters is a high priority in development
and settlement decisionmaking.
South Australia encompasses a substantial portion of the plains
which in geological times were covered with ocean. The soil's
high salinity content thereby contaminates both below ground
and on-ground water sources.
Rain water becomes a desirable source of unpolluted waters;
however air pollutants and pollutants on run-off surfaces
particularly in urban areas further contaminate this water
source. Low rainfall levels in the region becomes one of
the natural land capacity limits where in the past development
of greater density now depends on importation of waters from
elsewhere.
Major watershed diversion schemes and pipeline distribution
have been undertaken in the past to make large portions of the
region habitable.
In addition to their energy and recurrent maintenance demands,
there is doubt about the sustainability of this approach to land
settlement in the long term.
Already large areas of irrigation abutting rivers has increased
held salinity levels; and areas cleared for grazing abutting
riparian zones of some streams have become salt logged and
unuseable.
Abutting urban areas waste and stormwater pollutant discharge
has measurable detrimental effects on swamp and ocean areas.
Environmental projects limit the use of land to
within occupancy levels where local resources, particularly
water supply, will suffice.
This includes allowing for poor rainfall periods, drawing on
on-ground and in-ground sources only to the extent where
replenishment from local good season rains is then possible.
Water use strategies within developments become integral to
such regional development philosophy, in particular low water
use appliances, waste water treatment and re-use, and disposal
of waters to avoid land damage.
This particularly includes development design to avoid changes
to in-ground waterflows (underground courses), avoid
concentrations of stormwater flows and nutrients and
contaminants in waste waters.
Development creates roof and pavement areas where previously
natural soil absorption dissipated water flows. Concentrations
from such hard surfaces need to be dealt with to avoid damage
to land elsewhere.
Conventional stormwater systems pipe such damage sizeable
distances from collection points in concentrated and high
flow speed form.
Environmental projects therefore consider water in
categories including:-
- potable waters -
from unpolluted collecting surfaces or where
basic treatment including UV filter suffices
- stored waters -
from mains or on-ground sources where carbon
filter restores potability
- stormwaters -
from traffiked surfaces, where treatment even
with carbon filter may not restore potability
- grey waters -
waste waters from bathroom, kitchen, laundry
where grease trap and biological treatment
achieves standards suitable for garden watering
- black waters -
septic waste waters unsuitable for human contact
and requiring disposal segregated.
With seasonal water generation, rain water too becomes a
stored water, though usually in covered tanks limiting
contamination by salinity or pollutants; although tanin
from Australian native vegetation retained on collection
surfaces can colour and taint taste.
Development practice therefore includes:-
- screens to gutters
- maintenance obligations to clear collection surfaces
- 'first rain' diversion piping and syphon delivery piping diversion and cleaning pipes
- filters
Sizing water storage is limited by available rainfall and
roof area. Some calculations allow for top up by out of
seasonal rain thereby reducing storage volume required.
This approach doesn't allow for storing opportunity water from
higher than average seasons against use in drought conditions.
Rain water systems will include mixtures of delivery/storage/
supply infrastructure complete with gravity feed and pumped
sections. These need to be matched to other development features:-
- There is limited size to DC electrical motor pumps
suitable to operate from renewable energy systems without inverter
- various appliances have varied pressure requirements
- while pressure hot water services will operate at low pressure
(<20psi) some low flow shower heads (particularly with aerating
heads) require high pressures (>60psi).
A compromise between
delivery pressure and water saving can be made (removing
some of the waterflow restrictors in such a showerhead).
- water saving strategies includes the use of pressure
balancing tap systems, dual plumbing to allow connection by
separate rain water and bore water supplies
- waste water treatment and re-use is described on the separate page
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