Some notes on the various geological points raised above:
Ripon lies above a bed of gypsum (Calcium Sulphate), which is a more soluble rock than limestone and chalk (Calcium Carbonate), hence the ever-present hazard of collapses into what must be sizeable caverns eroded in it. Luckily they do not occur very often; but events like that photographed are not predictable.
These two minerals do not dissolve very well in pure water but even very weak acids corrode them. Rain-water is always naturally slightly acid from dissolved atmopheric CO2 (irrespective of anthropogenic additions), and can pick up more acids from organic material in the soil.
Water from a Chalk aquifer is likely to be safer than that from the more massive limestone, because Chalk tends to be fractured into innumerable small blocks separated by extremely fine fissures. This structure slows the overall flow through it and improves the filtering effect. A chalk aquifer is somewhat similar to one in gravel or sand; with diffusive, very long flow times.
Massive limestones (e.g. the Mendip Hills, Pennine Hills) host much larger conduits dissolved along joints and bedding-planes; including conduits developed to sizes humanly explorable as caves. There is not a water-table as such across the entire structure. Nor much of an aquifer though some water is trapped in overlying soil, peat hags or gravel deposits for slow release into the conduits. Consequently the water flows through from stream-sinks and soil-cover on the hills, to the risings, quite rapidly, typically in only a few days; and still bearing any micro-organisms, organic decay products or other potentially harmful additives it washed underground. It is still in contact with the rock for long enough to absorb some of the soluble minerals, though.
Both types of rock are chemically much the same, giving “hard” water. Hardness concentrations combined with flow studies are used in estimating landscape-lowering rates of Limestone and Chalk hill ranges: for example the rain dissolves away about 28 000t/yr from the Mendip Hills. That can fur a lot of Somerset kettles, showers and model loco boilers!
Underground water oozing from surface to spring does not spend “millions” of years down there, but can take very long times to emerge. Though such water might be biologically “clean”, in some areas it might carry metallic salts it has found, although I don’t know of anywhere where this is a health problem. Mineral salts tend to flavour the water, so would be noticeable if too strong. A spa in the village of Radipole, near Weymouth, did not last long because the water is unpleasantly sulphurous from contact with the Kimmeridge Clay – even Regency fashions had their limits!
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The water supplying Weymouth and Portland comes from Chalk aquifers overlying Limestone then Clay. The original pumping-station drawing from the source of the River Jordan (no not that one!) at Sutton Poyntz has been preserved as its own museum though open only occasionally or by special party booking. The displays include a framed certificate completed by the Sanitary Inspector early in the last Century, for a farm’s drinking-water well. He noted that the water was discoloured, and after recording what he found in it, concluded it would be eminently suitable as liquid fertiliser!