水的酸碱度是由水中溶解的矿物质决定的。 天然的水里往往含有钾、钙、钠、镁、偏硅酸等多种矿物质，多呈弱碱性。而不含这些矿物质的水往往呈酸性。因此，通过测试水的pH可以直观判断水中是否含有天然矿物质。

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