This question probably suited to a UK answerer - I get Kidney Stones
every few years. Some pass, (with the associated pains) and others are
accumulating to be "done" at some point in the future. Meanwhile I
meticulously buy water in 2 litre bottles to ensure I drink at least
1.5 bottles a day, every day. A geologist friend has now told me that
SOME bottled water would have higher accumulations of the very
chemicals that go into the stones than normal tap water. I live in a
chalky hard-water area and the tap water is disgusting. WHAT should I
avoid in bottled water and WHICH brand would be best.

As someone who has suffered from several kidney stones, done research
on my own, and seen two specialists, I can tell you that your
geologist friend is incorrect.  He is thinking of a kidney stone like
a stone in nature, while kidney stones are generally calcium oxalate
or uric acid.  Minerals in water will not lead to kidney stones. 
Actually, drinking water is the best thing you can do to help prevent
the dreaded pain.

Your friend is incorrect. Preventing formation of kidney stones,
depend on what type of stone your body is forming. Calcium Oxalate,
Urate, struvite etc... Most research on the etiology and prevention of
urinary tract stone disease has been directed toward the role of
elevated urinary levels of calcium, oxalate, and uric acid in stone
formation. Hypercalciuria (higher than normal calcium in urine)is the
most commonly noted metabolic abnormality.Magnesium and especially
citrate are important inhibitors of stone formation in the urinary
tract. Decreased levels of these in the urine cause a predisposition
for stone formation.The most common findings on 24-hour urine studies
are hypercalciuria, hyperoxaluria, hyperuricosuria, hypocitraturia,
and low urinary volume. Other factors, such as high urinary sodium and
low urinary magnesium concentrations, may also play a role. To
identify these risk factors, a 24-hour urine profile, including
appropriate serum tests of renal function, uric acid, and calcium, is
needed. Such testing is available from a variety of commercial
laboratories. Having minerals in the water is not the reason for stone
formation.

For almost all patients in whom stones form, an increase in fluid
intake and, therefore, an increase in urine output is recommended.
This is likely the single most important aspect of stone prophylaxis.
The only other general dietary guidelines are to avoid excessive salt
and protein intake. Dietary calcium should not be altered unless
specifically indicated by 24-hour urinalysis findings. Urinary calcium
levels are normal in many patients with calcium stones. Reducing
dietary calcium in these patients may actually worsen their stone
disease, because more oxalate is absorbed from the gastrointestinal
tract in the absence of sufficient intestinal calcium to bind with it.
This results in a net increase in oxalate absorption and
hyperoxaluria, which tends to increase new kidney stone formation in
patients with calcium oxalate calculi.

As you can see the subject is rather complex, so you should consult
your physician, above should not be considered professional advice.

The Italian mineral water Fiuggi has quite a reputation for helping
eliminate kidney stones.

://www.google.com/search?hl=en&q=fiuggi+kidney+stones&btnG=Google+Search