本文想探討「淡水」、「淡水河」名稱的起源及文意涵的變遷，亦即「淡水」在十五、六世紀爲何成爲漢人對於北部台灣的稱呼？漢人又是如何認識北部台灣最主要的一條河流－淡水河？換言之，這兩個名詞的出現、使用與內涵的變化，反映的是漢人對於台北地區的認識，從簡到繁，從海口到腹地。全文主要分爲兩個部分，先探究淡水地名起源；進而再論述漢人認識淡水河的過程。本文認爲，淡水一詞的出現應在十六世紀的下半葉，最早是因東亞航路的發展，漢人發現台灣島北端的雞籠，進而因貿易、捕魚與航行取水的關係，發現雞籠西南方的港灣－淡水，而且淡水出産硫磺，漢人紛紛來到淡水採硫，使得淡水廣爲漢人知曉。十七世紀末，漢人大量移民來台，對淡水的了解不再止於河口，但進入台北盆地後，對淡水河的地理觀念，卻形成「江有二源」的論述傳統。十八世紀時由於漢人進入淡水河流域各河段開墾、定居，因此出現了區域性的溪名，本土化的結果，使得傳統江有二源的說法不足以解釋現狀而趨於沒落。到了十九世紀，外國傳教士、學者、官員先後來台，他們稱呼北部台灣的首要河流爲淡水河，而三條支流分爲被稱爲雞籠河、新店河與大嵙崁河，此一看法爲日治時代的統治者接受，透過政府力量，使得淡水河及其支流的論述與命名從此確定，並沿用至今。

In the historical documents about Taiwan, the term 'Tamsui' (淡水) is an important geographical name for indicating the most famous region of northern Taiwan. This paper tries to research the origin of the place name 'Tamsui' and how the Chinese defined it in different times. The author argues that 'Tamsui' as a nautical term means fresh water which is a requirement of life during the voyage. For recollecting the location of fresh water, the Chinese sailors named the place 'Tamsui'. The northern Taiwan was conveniently located on the shipping line between the Ryukyu Islands and the Fokien provine. The climate is moist. Naturally those sailors came here for fresh water and called this region as 'Tamsui' in the sixteenth century. During the seventeenth and eighteenth century the Chinese migrated to Taiwan. They colonized Taipei Plain and expended the conception of 'Tamsui' as a river name. But in that period their description of the river was different from ours. They considered that the river had two main branches In the second half of the. nineteenth century those foreigners visited 'Tamsui' and wrote down what they had seen. They gave a different description that the 'Tamsui' had three main branches. Nowadays we continue using this modern conception.