Clean and Inspect Gutters and downspouts for blockage and leaks. Remove leaves and debris, do not wash material down the downspout.
Test your drain system for blockage. Insert a garden hose into your downspout and let the water run for 5 minutes. Check to see if the system can carry off the water and that your basement is not getting wet as
the result of a broken pipe.
Inspect the soil slope from the foundation. Water should run away from the foundation for at least 48". This will help eliminate the possibility of water pooling against the foundation.
Test for a water supply line leak or break. Check sinks for drips, toilets for leaky values, etc. If you have city water, find the water meter, normally at the curb, and take an accurate reading. Wait 1-2 hours and check if the meter has changed while all water has been turned off
Test basement walls for seepage.Tape a 12" square piece of aluminum foil to the moisture prone wall making sure all sides are airtight, wait a few days and check the foil. If moisture is on the outside it is condensation, if it is on the inside it is seepage.
Check for water leaks where the pipes enter the basement.