By Fabian Hamacher
ITU ABA, South China Sea (Reuters) - On Itu Aba, in the Spratly archipelago of the South China Sea, Taiwanese coast guard officials proudly haul a small wooden bucket of water from one of several simple concrete wells on the coral outcrop.
The water, clear and sweet tasting, is key to Taiwan's argument that Itu Aba is legally the only island among the hundreds of reefs, shoals and atolls scattered across the hotly disputed region.
Itu Aba, which the Taiwanese call Taiping, is coming into focus as the Philippines challenges the legality of China's claims to most of the South China Sea.
"Usually from Taiping Island we can see Chinese and Vietnamese fishing vessels," said Wang Mao-lin, a senior coast guard official, who has been stationed there for a year. He said the coast guard would shoo the vessels away.
As part of a case now being considered by an international court in The Hague, the Philippines has argued that no feature in the Spratlys could be legally considered islands because they lack the ability to sustain human habitation or economic life.
But if Itu Aba is determined to be an island, it is entitled to a 200 nautical mile (370 km) exclusive economic zone under the United Nations Convention on the Law of the Sea (UNCLOS).
Such a ruling would complicate territorial disputes across the vital trade route and resource-rich region, where Malaysia, Vietnam and Brunei also have claims.
The Philippines presented its case to the judges' panel of the Permanent Court of Arbitration in November and a ruling is expected in the next few months.
CHINA SAYS CASE INVALID
China has refused to participate in the case, saying it is invalid and the panel has no jurisdiction. Taiwan, which China deems is a breakaway province, is not a member of the UN and not a signatory to UNCLOS.
Taipei is instead waging a propaganda campaign on Itu Aba, including a high-profile visit by President Ma Ying-jeou in January and Wednesday's first ever visit by international journalists.
The group, which included Taiwanese journalists and local scholars, was shown vegetable gardens and plantations of coconuts, sweet potatoes and papayas.
Along with scores of chickens, the gardens provide food for the almost 200 people who live there, mainly coast guard personnel, Taiwan officials said.
Serviced by a 1,200 m airstrip, other features on Itu Aba include a hospital, solar generators, a temple, wharf and a lighthouse.
Ma, in a briefing held in Taipei with returning media, extended an invitation to the Philippines government and tribunal members to visit to Itu Aba.
"I, as Republic of China president...formally invite the Philippines government to send a representative or lawyer to visit Taiping Island," Ma said, referring to Taiwan by its official name.
While Taiwan has occupied the 46 hectare (110 acre) outcrop almost 2,000 km south of Taipei for decades, China, the Philippines and Vietnam also claim it.
ROCK VS ISLAND
Tensions in the region have been on the rise, with Beijing and Washington trading accusations that the other is militarizing the region as China expands its reclamation and construction activities on several reefs while the United States undertakes more freedom of navigation patrols and overflights.
Asked about the visit to Itu Aba, Chinese foreign ministry spokeswoman Hua Chunying said the Spratlys had been Chinese territory since ancient times.
"Chinese people on both sides of the Taiwan strait have a responsibility to protect the Chinese people's property handed down from one's ancestors," she told a daily news briefing.
There is construction work on the Spratly islands China occupies at present, but when conditions are right China will consider taking reporters there, she added.
Ma on Wednesday said that recent land reclamation and military-type activities by China "have nothing to do with us."
Under the relevant international law, islands must be able to "sustain human habitation or economic life of their own".
Other features are classed as "rocks", which can claim 12 nautical miles of territorial waters, and "low tide elevations" which can claim neither.
Arguing its case, the Philippines questioned the quality and quantity of water on Itu Aba and said no Spratlys holding had ever been home to an indigenous population.
Military garrisons, supplied from the outside, did not count, they said.
Independent legal scholars and experts told Reuters that Itu Aba could prove a potential sticking point in the broader case.
"For decades, the combined wisdom among scholars studying the South China Sea is that Itu Aba is the only island in the Spratlys," said Ian Storey, a regional security expert at Singapore's ISEAS Yusof Ishak Institute.
The limits of UNCLOS mean the judges cannot rule on sovereignty, but instead on the entitlements from certain features and the rights of the Philippines within its own economic zone. A ruling would be binding, but difficult to enforce.
A source close to the Philippines' side said Manila's legal team was aware that the status of Itu Aba was one of the thornier parts of the case.
"We've asked the tribunal to determine the nature and character of the different features in the South China Sea so it's up to the tribunal to decide on this issue," Charles Jose, a Philippines foreign ministry spokesman, said on Wednesday.
(Additional reporting by Greg Torode in HONG KONG, J.R. Wu in TAIPEI, Ben Blanchard in BEIJING and Manuel Mogato in MANILA; Writing by Greg Torode; Editing by Lincoln Feast)