THE WATER OF THE COMMUNITY
The water of the community
People – islanders – can arrange part of their water procurement themselves, having a private well, harvesting rainwater, water slimming. That is very good but not the subject of this lecture, which is how to understand, design and develop the common freshwater system of the community.
The water system includes the catchment; raw water mains; the water treatment plant; pumping stations; transmission mains; the storage of water in reservoirs, cisterns and tanks; bulk, district, zone and domestic meters; distribution to domestic, agricultural and industrial users, and in the end, how to finance and administrate it all.
We will look at common water treatment, water distribution, wastewater and water management. We will give you some examples, before inviting you to do it yourself.
Potable water resources
As a consumer, you do not constantly think about where water comes from. You get water piped to your home and delivered to a tap or spigot and assume the water can be consumed safely as it has passed adequate treatment and meets drinking water regulations.
On an island, life is slightly different: we have lots of saline water (we are surrounded by it on all sides). But we don’t find enough freshwater easily.
Vis, a Croatian island in the Adriatic Sea, 55 kilometres from the mainland, covering a surface area of 90 km2. It has three hill chains and two valleys. The highest point of the island is Hum at 587 m above sea level. Rock is composed of cretaceous limestone and dolomite; Triassic and clastic rocks.
Vis has a Mediterranean climate with long and hot summers. Years without rain for 3-4 months are not rare. Winters are mild (average January air temperature is 100C), the average yearly rainfall is 800 mm. There are no surface water flows except after heavy rainfall (typical for Adriatic islands).
The groundwater formation is estimated at approximately 400 mm and takes place almost completely during the winter. The groundwater flows quickly into the limestone that dominates the island's bedrock and the groundwater surface is very close to the sea level, which is not usually normal in, for example, granite bedrock. This indicates a major problem in obtaining freshwater from the island's groundwater.
3,460 persons live in the island’s two municipalities. Ten times the population comes to visit every year = 36,750 tourists, spending some 200,000 days on the island. The pressure on the island's freshwater system is not so high, the total demand is about 139,000 m3 per year.
The leaks in the 85 km-long distribution system account for about 25 % of the water use.
The water supply system of the island uses two sources of drinking water: drilled wells in Korita and the fresh water spring of Pizdica. The Korita pumping station is located in the interior of the island above five drilled wells containing water at a depth of approximately 160 meters. Water is pressured into a pumping pool from where it is distributed to consumers (20 l/s). The Pizdica spring is located in a gallery drilled in solid rock close to the shore in the bay of Komiža, deep into the Hum mountain.
Cross-section of Vis: Observe the solid black line representing the groundwater level in the rock. Typical of limestone rock, groundwater flows quite quickly out to sea. The fresh - salt groundwater boundary is just below sea level, meaning the fresh groundwater magazine is not big. To prevent salty groundwater on Vis, great caution is needed when pumping groundwater.
To visit Pizdica, you leave the road at a height of about 250 meters and descend on a pathway which becomes a serpentine trail down the mountainside. The route becomes more rugged, and you can easily slip on the simple stairs and plateaus. There are wild roses, blackberries, hedge flowers, rosemary and St. John's wort. Through many turns, bends and staggering dumps, you eventually land on a beach with decayed buildings.
Vis was a floating fortress with bunkers and caves for torpedo boats during Yugoslav time. No visits were allowed. The Pizdica source was the only known natural water resource of the island and therefore carefully guarded by the military, who had a posting there and carefully guarded it from attacks of all kinds. Two iron doors, 50 meters apart, close the double entrance to the spring, connected by a crescent-shaped gallery, designed to bear the pressure of a 500-kiloton bomb. A heavy steel door leads into today's pumping room, where a small side door leads through a long narrow tunnel deep into the mountain, with the water pipe from the source on the floor. It is dark with simple lamps every ten meters. The passage turns once more. The pipe has taps into the mountain. You hear the water gurgle, and, after another bend, you are at the source.
It is a small basin, 2 x 2 meters, one meter deep, giving 4 litres per second during summer, 3-4 times more during wintertime. The water is cold and clear and tastes a little salty.
It is spectacular. First the steep descent, then the oversized steel and concrete defence of the source, followed by today's impressive engineering solution to extract the water of the source, and finally, at the bottom of the mountain, the ancient, mysterious source, the origin of all life, the holy water. The Croatian word Pizdica literally means "small vagina” and the spring is referred to as “the pussy fountain”.
From an engineering point of view, drinking water is a precious provision which has to be found, extracted, purified and distributed among us humans. From a more poetic perspective, a freshwater spring is not only a subterranean spring but also a subconscious, important source of legends, dreams, nightmares, poetry, music and myths.
Except for groundwater, seawater can be used if run through a desalination process described below and we can use rainwater harvested on roofs or yards and flowed through a gutter leading to filters that, depending on their properties, may retain particles from the size of leaves, pebbles etc. down to the size of dust. Then the filtered water goes into a storage tank (reservoir) that is usually built into the ground or placed in the basement with a storage temperature ideally below 18 °C.
Rainwater is suitable for non-drinking use, i.e. toilet flushing, cleaning, watering and, if thoroughly filtered, also in industry. It can be used for drinking, provided it is properly disinfected by UV lamps, chlorination, ozonation etc.
Ithaka is an island of 96 km2 in the Ionian Sea. It largely consists of a series of folded Jurassic to Eocene limestones. Its western side is arid and steep, and its eastern side is green and accessible. It rains mainly on the eastern part of the island, as the west side is in the "rain shadow" of Kefalonia. The winter precipitation is high, about 600-700 mm and allows for abundant groundwater formation in the eastern part of the island. However, the limestone mountain offers limited groundwater magazines. Most of the water flows relatively quickly to the sea unless sealing bedrock layers are varied with limestone. The withdrawal opportunities may be average in some places for these reasons.
The groundwater surface is rather low even though large parts of the island's land surface are much above sea level. This causes problems with groundwater outlets in wells, as the outlets further lower the groundwater and thus increase the risk of water becoming salty.
The resident population is 3,100. Technically speaking, recalculating the impact of summer residents and visitors, the human pressure on the island is equivalent to 6,182 all-year inhabitants.
On a winter day, the people of Ithaka need 250 m3 of water, and on a hot summer day when water consumption peaks, 1,000 m3. By tradition, islanders collect rainwater during winter and store it in tanks under their houses for summer use. Some 90% of the active dwellings on the island have cisterns of 20-150 m3. It seems that the municipality of Ithaca produces 67 % (165,000 m3) of the total yearly amount of water needed on Ithaka, (247,000 m3), indicating that the islanders’ use of rainwater equals one third of the demand.
The municipality has built four wide rainwater collectors, but frequent small-scale earthquakes are destroying them.
Another source of water is our own wastewater. Water is not consumed, it is just used. There is more wastewater than ever and over 80% of the world’s wastewater is released without treatment. After treatment, wastewater can be reused for irrigation, aquifer recharge, industrial processes, heating/cooling, and as potable water.
Potable water treatment
Some freshwater requires treatment before use, sometimes even water from deep boreholes, wells and springs. Some of the disinfection treatments it is subjected to include techniques such as filtration, chemical treatment and exposure to ultraviolet radiation (including solar UV) to reduce levels of waterborne diseases.
We can treat water by boiling which kills waterborne pathogens but this requires abundant sources of fuel, and can be very difficult for consumers, especially where storing boiled water in sterile conditions is hard to achieve.
Desalination is a type of water treatment, very appropriate on islands with access to immense volumes of saltwater. It involves the following steps: the seawater is transferred to the desalination plant through large pipelines (intake). The water is filtered to remove debris and floating particles as a pre-treatment. Salt is removed with the use of semi-permeable membranes and high pressure in a process called reverse osmosis, a method widely applied to separate salt from water. The process is very energy-consuming.
Desalinated water is further treated mainly to avoid corrosion in pipes and taps, to avoid bacterial infection, or to improve its taste by passing it through carbonate rocks (post treatment). The water finally enters the distribution network. The output volume of desalinated water is approximately one third of the incoming volume. The remaining water is used in the operation of the plant and includes the high salinity brine which is discharged back to the sea.
Desalinated water can supplement municipal water supplies and it is also used in industry and irrigation. The limitations for using desalinated water for irrigation are mostly economic, as it is very expensive to produce. Furthermore, with the minerals removed, its suitability for irrigation has been questioned.
Water treatment can also include running imported water through UV filters, as is the case with the water shipped to Inis Oírr, or treatment of the water that has been pumped through the 160-kilometre long pipeline to Vis.
After treatment, water is stored in reservoirs and fed to the consumers by gravity or by pumping through pipes. Pipes are generally laid below the road pavements, and, as such, their layouts follow the layouts of the roads.
Leakage of untreated and treated water from pipes brings high costs to the system and reduces access to water. Leakage rates of 50 % are not rare in water distribution systems.
Distribution can also be non-piped: water trucks, bottled water and simply fetching water with a bucket from a village pump.
Let’s revisit Houat, a commune in the Finistere department of Brittany. There are 242 people registered as permanent residents on Houat, there are 600 summer residents and some 500 people visit the island for one day during the three-month summer season. The human pressure on the island is 202,330 person-days but, as always on islands, very uneven, peaking in summer when water is scarce. A hot day in July, almost 1,000 visitors, plus 600 summer residents, plus 242 all-year residents can be on the island = 1,842 p/2.9 km2 = 635 p/km2.
Data from the municipality reveal that a resident household on Houat uses 70 m3 of water per year on average. The total water demand can be estimated at 13,238 m3.
Running municipal water was installed on Houat in the 1970s, using rainwater, a well and a spring. These were supported by a reverse osmosis desalination plant with a capacity of 50 m3/day, providing 20 percent of the needs of the island, being estimated at 100-120 m3/d.
In the 1980s, a search was undertaken for additional water sources. Four 50-meter-deep drills were made. Three of these were put to work, the fourth one contained excessively salty water. In 1990, a new 100 m deep drill was made next to the stadium which is today the island’s main source of water.
The water from these drillings is pumped to a raw-water reservoir holding 2,600 m3 of water, processed through a filter system and then stored in 4 reservoirs of 2,500 m3 each, close to the raw-water reservoir. In two water towers of 200 m3 each, located above the castle ruins, potable water is stored before distribution. The water is distributed through a pipe network covering all households. The cost of this infrastructure leads to a water price on Houat of 2.06 euro/m3.
Water management is about developing, leading and controlling the use of water resources. It includes personal, local, industrial, community, municipal, county, regional, national and international responsibilities as laid out by law, regulations, directives, practices and budgets.
It is a sub-set of water cycle management. Ideally, water management planning takes into consideration all the competing demands for water and seeks to allocate water on an equitable basis to satisfy all uses and demands. In practice, this is not an easy task.
If water shortages are present, water management includes making difficult decisions about how to allocate water resources. Utilities may limit availability of water to certain times of the day to cut down on usage and citizens may be encouraged to conserve water as much as possible. Fines and tiered pricing structures can be used to penalize households with high water usage to promote conservation.
In addition to considering the needs of individual consumers, people in charge of water distribution must think about industrial and agricultural resources of water. Interruptions of water supplies can result in costly delays that may have a ripple effect.
In the end, it all has to be financed and administrated, too.
Lastovo is an island of 47 km2, located 50 kilometers out in the Adriatic Sea, where almost everything is 46: the area is 46 km2, there are 46 churches, 46 fields, 46 beaches/bays and 46 islands/islets. The 792 islanders live in six villages. With visitors and summer residents, the human pressure is equivalent to 1,509 residents. Lastovo is the most remote of the Croatian islands and remoteness creates some disadvantages, such as time-consuming transports and high prices, but also some advantages: a well-developed public service, very clear blue waters and very clear skies. The island is situated in a clear blue sea with 50 metres visibility and boasts to be one of the least light-polluted places in the world.
Lastovo obtains its freshwater from three sources:
1. A mainland pipeline from 1982, a submarine pipeline built by a Norwegian company from Korčula to Lastovo over the 80-metre deep, flat, sea bottom from Korčula, 17 km away. The water originates from the mainland and comes via pipeline from Neretva to Pelješac over Korčula to Lastovo, where it is fed into the reservoir at Sveti Luka. The water is thus transported 160 km in total.
2. The inhabitants of Lastovo collect and use rainwater to a large extent.
3. The main water supply system of the island of Lastovo is based on the use of three drillings in Prgovo. 5 l/sec of water is processed through the desalinization plant in Prgovo field. The desalinated water is pressurized to the central water reservoir, from which the water is further gravitationally transported to other reservoirs on the island. The desalination system works mainly at night and fills the main island water reservoir so at daytime it is under a pressure of 3 to 5 bar.
Lastovo needs 51,000 m3 liters of freshwater to meet the human pressure on the island, but produces 73,304 m3 of which 30,645 m3 is lost in leakages. The consumption of municipal freshwater is 42,659 m3 and the rest is obtained through rainwater collection, about 25 percent of the demand ~ 15,000 m3, plus water for the animals.
Lastovo is a municipality and has a technical director who is responsible not only for the procurement of water but also for calculating its consumer price, which is 2.77 euro (1.5 euro + VAT) per m3 for residents:
There is also a sewage charge of 30 %, meaning the price for the consumer will be 20.23 kuna = 2.77 euro.
The 1992 UN Dublin Statement on Water and Sustainable Development stated that:
1. Fresh water is a finite and vulnerable resource, essential to sustain life, development and the environment.
2. Water development and management should be based on a participatory approach, involving users, planners and policy-makers at all levels.
3. Women play a central part in the provision, management and safeguarding of water. Institutional arrangements should reflect the role of women in water provision and protection.
4. Water has an economic value in all its competing uses and should be recognized as an economic good.
It was followed by the European Commission Water Framework Directive in 2000.
Our project, and this website, in a simple form, address the issues of water management with a special focus on islands.