I've answered about the impact of drilling a well on water table, which is the most important aspect.
But your question includes also an aspect of water quality. These two aspects are sometimes contradicting each other. If the water source is plentiful, one well should be enough. Otherwise, consider two wells:
- The drinking water one located at a higher place to minimize water pollution. Far from the gray-water recycling and/or humanure lot, etc..
- The lower quality well for irrigation and bigger volume output.
The wells should be far enough from each other so that the lower one wouldn't significantly drain the one above. This can be avoided by deeper drilling.
And both wells should be used regularly to prevent 'clogging'. It can take some time until the underground water makes its path to supplement the water requirements of the well. When the well isn't used for certain time, those paths can detoriate.
If it's possible, build a tank or a retention basin to keep the rain water for irrigation. It's the most sustainable way of using the rain water.
Even if it could seem as a good idea I wouldn't join the retention pond with the well. Mixing the surface water with underground water can pollute the underground water.