Sometimes if the weather has been hot and you haven't been able to water regularly the compost in your pots can get very dry. Mostly if you water it well all will be OK, but sometimes the compost can get so dry that no amount of water from the top only will wet it again.
In order to check, after watering lift up the pot and see if it feels heavy enough, if it doesn't then you likely have a problem. The solution is to get a bucket or bath of water (or a wheelbarrow full if dealing with lots of pots) and put the whole thing in that for about an hour - if the compost is super dry you may need a brick or stone to weigh the pot down as it will have so much air in it that it floats easily.
In order to check, after watering lift up the pot and see if it feels heavy enough, if it doesn't then you likely have a problem. The solution is to get a bucket or bath of water (or a wheelbarrow full if dealing with lots of pots) and put the whole thing in that for about an hour - if the compost is super dry you may need a brick or stone to weigh the pot down as it will have so much air in it that it floats easily.