These are pretty standard recipes for preparing hard water samples for lab-investigation purposes:
To prepare Temporarily Hard Water
Take Fresh LimeWater (saturated calcium hydroxide - shake a few grams of Ca(OH)2 in a litre of water, shake it occassionally over a day and leave to settle, pour off the clear solution on top); Bubble carbon dioxide gas through the limewater (CO2 can be easily generated by adding dilute acid to some carbonate (eg. baking soda, sodium bicarbonate) in a standarg gas-generation flask set-up).
Bubbling of CO2 through limewater first turns it milky, then after a prolonged period of bubbling, it turns back to clear once again. This is your Calcium bicarbonate solution - which can be used as temp. hard water for all of your purposes.
(Ca bicarbonate is not a stable compound and cannot be isolated in a pure solid form - you wouldn't find a 'bottle' of that stuff and make up its solution.)
To prepare Permanent Hard Water,
Dissolve calcium chloride or magnesium sulfate (or both) in water, (about 0.1 M should be sufficient)
To prepare Hard Water similar to naturally occuring ones, Take 3 volumes of the temp. hard water and 1 vol. of the perm. hard water and add 2 vol of dist. water. That should give a pretty good mixture, if it is found to be too weak, omit the dist. water.