No, it isn't, but not because of the solar panels.
If you have access to municipal water, there's no economically viable way to make rainwater potable. Roughly speaking, rainwater is about as dirty as "grey" waste water (from sinks, showers etc.) and it needs a similar amount of processing before (re)use. Rainwater contains all kinds of pollutants from the air plus whatever gets leached from your roof and gutters, so it's not really clean in any sense.
There are many possible uses for treated rainwater and grey waters, with each successive level having more stringent requirements (and thus being several times more expensive):
Garden, toilets: You only need to remove solid particles (tiny grains of sand and the like) to prevent clogging your toilet tank fill valve and to make sure the water's not too smelly (you don't want your toilet to smell worse after flushing than before, which is what happens if you use stale water). You just need to make sure you store the water in an underground tank (constant low temperature), don't store it for too long (2-3 weeks maximum) and use a simple filter.
Washing clothes: More filtering (carbon filter) needed to prevent clothes from getting discolored and really smelly.
Showers, baths, sinks: Need to eliminate bacteria and viruses. There will be lots of them in the tank and your shower will gladly disperse them into the air and you will be breathing them, with unpleasant results. You thus need UV treatment, ozone, or chlorination.
Drinking and cooking: You need to get rid of all kinds of dangerous metal ions, nitrates/nitrites, carcinogenic micrometer-sized dust particles, volatile organic compounds, chemicals leached from plastics and so on (this would also take care of whatever comes from the solar panels). This is a real technical challenge. Reverse osmosis or distillation is not an answer – it will remove all ions, making the water not potable. (Drinking distilled water will kill you pretty quickly.) Ion exchange columns won't remove small organic pollutants, and so on.
Given that water usage also usually decreases in this order, it usually makes sense to only do the first two levels. If you're in a really dry region where municipal water is extremely expensive or unreliable and/or you want your house to run super-green (even though it doesn't make sense economically), you can consider the third level (personal hygiene uses) as well. But making rainwater potable? Only if you really don't have any other source of water.
