This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
For Carbonic Acid. Add an equal part of lime water. If carbonic acid is present, a precipitate is seen. Add muriatic acid and it will effervesce.
For Hard Water. Dissolve good soap in alcohol; drop a few drops in a glass of water. If the water becomes milky, the water is hard. If it remains clear, the water is soft.