Vorovoro water system
From Tribewanted
Development of a water supply to suit our needs is currently under development. Several sources are being considered:
Rainwater
Rainwater harvesting certainly needs to be done at a more developed level - there is certainly a significant amount of rainfall on Vorovoro in the rainy season. The concern with this method is storing the water for the dry months and that water might become stagnant. However, it would appear to be the most sustainable away for collecting water - if it rains enough!
Desalination
Desalination has been put forward a couple of times by members as, next to rainwater, the most sustainable and efficient way of harvesting water on Vorovoro. We need to look at the positive and negative impacts of this kind of system - especially in terms of the impact on the marine life and what is doen with the brine.
Bore hole
Bore hole is something Tui Mali is very keen to look at as the other island are now using it. The machinery needed to dig a bore hole is now ready to come to Vorovoro, just waiting on the barge. Water from the earth is not sustainable in the short-term however it might work well as a back-up.
This paper attempts to summarise the potential options for water supply on Vorovoro.
Summary
An island population of 30 persons is nominally expected to consume 300ltrs water /day
Desalination Desalination while initially looking a workable solution does not appear feasible as the process does not readily suit the treatment of comparatively low volumes of water but it is acknowledged that single person (manually operated) desalination kits are available there are technical barriers to switching desal plant on & off on demand. The capital cost of desal plant is high, there is also regular maintenance to consider along with fuel costs. Waste from the plant is potentially toxic to marine life – disposal of the waste might prove to be problematic in the region around Vorovoro. Despite an initial encouragement desalination is not considered to be a viable option for our water supply.
Borehole A borehole may be possible, after all fresh water must be present in the island eco system otherwise there would be no vegetation. A potentially high cost of drilling has to be considered, it may also prove necessary to use a powered pump to draw up the water Care though is necessary to avoid over extraction, which would potentially destroy the island eco system.
Rainwater Rainwater harvesting is quite widely used for water supply in Fiji. It has the great advantage of being comparatively low cost, simple to implement & requires no power source.
Detail
Water demand: From observations on Vorovoro last Sept the net consumption of fresh water per head appeared to be about 10ltrs /day, giving us 300ltrs /day for a population of 30 people. That estimation contains an error term because during Sept 06 water at the tribe camp was in addition supplied from storage at Tau Mali’s homestead. This secondary supply source has recently been ceased, but I don’t think usage from that single somewhat low pressure tap (faucet) was signifigent compared to the 5 taps (running at somewhat higher pressure) attached to the tribe camp water supply.
Someone on the island should ideally attempt a current assessment of daily water usage by observing the total consumption over a period of at least 10 days (the longer the better) Divide the volume (ltrs) consumed by the average number of persons present in the camp over the period – the result of course being the average person /day consumption.
Desalination: First looks at the latter make it appear quite attractive – just stick a hose in the sea switch on the plant and lola clean fresh drinking water. Further investigation it is found that desalination plant is best suited to treating 1000 ltrs/day of water upwards, the treatment of smaller volumes not really being feasible with powered plant. The waste from a desalination plant has the potential to seriously disrupt the marine environment. The salt & other materials removed from the [sea] water will need to be disposed of somewhere. One_cannot simply pump it back into the sea. To do so would cause massive disruption to marine life including the coral.
It is possible to obtain compact manually operated desalination kits, these are often used on small boats. They feature a single use filter cartridge that is able to process around 10 ltrs sea water. Obviously the used cartridges need to be disposed of, they presenting similar eco hazards to the discharge from a more traditional (mechanically powered) plant.
It is not feasible to simply switch desalination plant on & off as required. Once commissioned the plant needs_to run continually 24/7 If the operating cycle is disrupted for any length of time, just a few hours in tropical climate, hazardous organisms will commence breeding within the filter membranes necessitating chlorine disinfection of the entire plant before it can be returned to service.
A desalination plant will of course require power. As previously explained the machinery requires to operate continually – meaning that fresh water produced in excess of requirements will run to waste. Obviously the power consumed by the machinery has also gone to waste – not an ideal state of affairs and completely at odds with our overall aims.
Power requirement for desal plant capable of 1000 ltr/day (sufficient to supply 100 persons) is estimate to be around 3 – 4 KVA The cost of a solar power system of this capacity would potentially be prohibitive - £10,000 +. A diesel set could be obtained s/hand for about £1500 but obviously will incur an ongoing cost for fuel (app. 30ltrs /24 hrs) We do not though want a diesel engine running continuously (if at all) on Vorovoro.
Borehole: A problem to guard against when drilling a borehole is over abstraction of the water. On a small island over abstraction of an underground water source is liable to result in the source becoming saline due to the infusion of sea water. Should this occur then vegetation that is dependent on that water will die. Recovery from such an event could take an extended period of time – outwith the lifetime of even the younger tribe members.
If the borehole is made with sufficient diameter (not trivial if the hole is of more then nominal depth) then the water can be brought up by rope & bucket. Otherwise some form of pump will be required. For a manually operated pump to operate satisfactorily the water will need to be no more then 15 – 20 mtrs down, ideally somewhat less.
One thing the lack of pumping effort will achieve is the prevention of over abstraction. Non the less competent professional advice will_be_essential before considering the commissioning of a borehole to ensure we do not risk permanent harm to the island ecology.
Rainwater harvesting: Obviously for this to work one needs rain. This is quite abundant on Vorovoro but only between Dec – March in any real quantity. The rain season is October – May but for the most part only nominal amounts fall at the extremities of the season.
With an island population of around 30 water consumption (at 10ltrs /person /day) is 300ltrs /day. To maintain supply for the (mostly) dry 8 months (243 days) will require the storage of some 73000ltrs. To maintain a sensible margin one should look to storing around 20% more – 88000ltrs. That would take a total of 9 tanks of comparable size (10000ltrs) to the main tank we presently have on the hillside by the toilet block. Obviously all the storage tanks need to be located at a similar level otherwise transfer logistics between tanks of differing levels may (almost certainly will) result in spillage.
Keeping the [stored] water in satisfactory condition may be a challenge but this may potentially be offset by the water collected being rather freer of general contamination than would be experienced in our more heavily populated domiciles. Storage of rainwater is quite widely practiced in the region, I have not personally been made aware of any specific problem and would not really expect any provided normal hygiene practices are followed.
The homestead features a pair of storage tanks, one of 12000 the other 30000 ltrs capacity. The larger tank is (according to reports received) filled by 6 – 7 days of heavy rain – it is not clear how continuous the rain is over that period. Our own collecting system (that I have not seen) is reported to recover 1000ltrs /hr. If we assume that for the “6 -7 days of heavy rain” referenced above it is actually raining for 50% of the time that infers our own collection system has comparable area / overall efficiency to that at the homestead. Someone on Vorovoro might care to verify this.
My feeling, but I am open to correction, is that the collecting area for a water storage system should be sized so that with average rain sufficient is collected to replenish 50% of the storage volume over a period of 3 – 4 days. Therefore we should plan to increase our present collecting area (assuming its performance is verified at 1000ltrs hr) by some 50% - more would be ideal if possible so as to maximise collection potential at the extremities of the rain season.
It should go without saying that the entire collection area should be located well clear of any source of contamination – the toilet block comes to mind here. It would also be most inappropriate IMHO to utilize the toilet block roof as part of the collecting area.
My idea of a collecting area would be to build a low level (but not too low) structure featuring corrugated roof sheets on the hillside towards the rear of the camp (with appropriate care the visual impact should able to be kept minimal) Means should be provided to be able to disconnect the water line(s) to facility the cleaning off of the “roof” without the wash water entering the storage tanks.
Atmospheric condensation: Making our own rain (in a bottle) It is potentially possible to try and condense water from the (somewhat humid) atmosphere of the region. Others are presently working on ideas to achieve this, hopefully an entry on the subject will appear here later.
Conclusions IMHO desalination is a non starter – it runs totally against the aims of our project and has no redeeming features whatsoever.
A borehole is potentially feasible, subject to a competent survey by environmental engineers. IMHO it would be ideally combined with another solution.
Rainwater harvesting has the huge advantage of minimal cost and is also an established solution within Fiji. Main disadvantage is a comparatively long (some 8 months) of no to very little rainfall. IMHO is a workable solution for a population of around 20 – 30 people. It would be best combined with an alternate solution.
Atmospheric condensation is a novel approach seeking to draw water from the (somewhat humid) atmosphere. Successful implementation may depend on island topology. Others are looking into this - may they please post their determinations on here
