Keep your soil moist by running a soaker hose 12 to 16" from the foundation and turn the faucet on 1/4 to 1/2 turn. If you have a gap, leave the water on until the gap closes. This may take hours or several days. DO NOT apply water directly into the gap.
Tree roots can also cause foundation movement. The roots will seek water anywhere it can find it. If it is very dry, it will pull water from under the foundation. You may need to root prune your trees. Simply watering may not be enough. They will consume more water from the soil that can be added by the sprinkler.