Fresh Water on Rapa Nui

There has been a lot of speculation on the problems of water supply in the remote past of Rapa Nui. “The Island has no rivers, creeks or valleys which wash its countryside nor water sources which refresh the thirsty”.. wrote Father Sebastian Englert in his book “The Land of Hotu Matua”.  And it is true that, previously, fresh water was a limited commodity.  But then there were no animals which needed to drink nor clothing, pots or other domestic articles to wash.  The Islanders got their supply from the volcanic craters of Rano Kau, Rano Raraku and Rano Aroi, which have, over the years, served as reservoirs for rain water. In a wet winter, from Rano Aroi, water will rush down several Ava or gullies toward the northeast and the southest.  This lack of rivers has not been a problem for a regular supply.  Several kilometers of subterranean caves, not always with easy access, hold an abundance of fresh water.  Rain water filters rapidly through the porous soil and keeps the water table replenished.  Water from the craters filters down until it bubbles up among the rocks near to the shore, places well known by the Islanders.
In the past, the natives built Taheta, rock depressions which served to hold water, and Manavai, rock gardens which maintained the humidity in the soil and protected the plants from the wind.  The only difficulty was in carrying water to distant places since there were no domestic receptacles except for gourds.

 

Today the Chilean administration has set up two systems for drinking water on the Island, one within the urban limits of Hanga Roa which covers the full population of the town and another in t he rural area around Vaitea. The town of Hanga Roa is supplied from two sources, the gully of Mataveri (Servicio Rano Kau) in the south and the area of Arapiki in the north.  The boundary between the two is Te Pito te Henua Street.  The water is pumped from subterranean layers found at more than 60 meters of depth and accumulated together with rain water.  There are four bore wells in use (Nbrs. 21, 25, 27 and 28) and one in reserve (N° 7)  (see map).  The water extracted from the wells is put through a chemical process in which chlorine is added in minimal quantities  (0.3 ppm to 0.5 ppm) to turn it into drinking water, as is required by the Superintendant of Sanitary Services (SISS).  Mario Zúñiga, head of the Sanity Division of the public services firm, SASIPA, tells us that : “The water contains many minerals and chemical substances which must be measured once a year.  According to the latest results from 2010, all meet the requirements.

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The prime water source on the Island is the rain, with a natural cleaning and filtering process through the rocky and sandy terrain, so it requires less chlorine than water on the continent.  To date, Rapa Nui has not had any cases of diseases or poisoning from the public water.

 

To regulate the flow of the water, there are five large holding tanks located on high points (two on Rano Kau, two on Arapiki and one at Puna Pau).  From there the water flows through a network of subterranean pipes to the houses.  Today the consumption is 4,000m3 (141,300 cu.ft.) of water per day, or 70 liters (18.5 gallons) per second. The demand varies with the number of tourists, which in high season can almost double that of residents. “In summer, the pumps are working 24 hours a day and, up til now, we haven’t needed to use the reserve wells”…states Zúñiga, and adds: “Within the contingency plans of SASIPA is a hydrogeologic study to determine the quantity and the quality of the water on the Island. In the case that we find that the sources of fresh water are insufficient, we will have to implement a desalination plant for sea water. Other projects approved for the coming year are the construction of a water system on Maunga Orito (140m – 460 ft. above sea level) as a back-up for the water supply in Hanga Roa, the replacement of pipes and mains with those of greater diameter to improve the volume and the pressure, the application of more modern technology and automation in the processes and, finally, the repair of the water works where we do the chlorification.”   The urgently-needed study for the installation of a sewage system and water treatment plant, to avoid possible contamination of the subterranean water table from the septic systems and outhouses that are found in most of the Island houses, has been postponed for the not-too-distant future.

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