The sources I am familiar with don’t discuss the water as much as they do the wine when it comes to drinking. The strength of the wine was set by the president at a symposium and it was mixed in a central crater to a ratio around 3 or 4 parts water to 1 part wine; thus making it roughly the alcoholic content of beer. Beyond that I know that Greeks preferred their water to come from natural springs and later on channels and cisterns were dug so that the supply could be pumped out to a larger area. I know considerably more about wine than I do about water so I can give you some background on that as well.

Wine was a huge part of the classical world and represented not just a drink but a social and cultural tradition practiced at every level of society. By the Mycenaean period viticulture had been firmly established in the Greek world and the spread of vineyards all over the Mediterranean was not because of ecological determinism but because it was a fundamental component of the classical world, they believed growing vines was an essential part of the Hellenistic tradition.

Ancient sources about viticulture are unfortunately mostly Roman based. We have a few sources from Greece, such as Athenaeus, but most of them that mention wine are discussing their use in medical remedies not the quality. We do know that most modern methods of training and pruning vines such as: trellising, propped vines, free standing bushes to growing vines up trees were known and mastered by the Greeks. It is impossible to know exactly what those wines would taste like, but because their practices in so many ways mirror modern ones in terms of cultivation and ageing there is a high likelihood that the quality and taste of high quality wine then would be similar to wines we drink today.

Where there might have been a greater difference from wine today was when it was produced in great volumes cheaply for mass consumption. Wine quality was determined and probably still is by climate, type of soil and the kind of vine you are growing but how it is aged is a big factor as well. It was usually agreed that wine that was unadulterated and aged for years was the best quality; but Pliny tells us a long list of additives that people used to age wine faster that suggests cheating a bit was a fairly common practice. One method that was apparently common was keeping the barrels in lofts above hearths.

Source

The Oxford Classical Dictionary. 3rd Revised Edn. Edited by Simon Hornblower and Antony Spawforth