basement
#1
#2
Huge subject. The best answers are on the outside of the house. Gutters, downspouts, landscaping, irrigation, and the slope of the ground around your house are huge factors -- keep the water away from your house. See if you can solve the problem with these simple inexpensive things first. Only if that fails should you consider more expensive solutions such as coating the outside of the foundation and installing a exterior french drain.
The details depend a lot on the type of your foundation and the seriousness of your problem.
The details depend a lot on the type of your foundation and the seriousness of your problem.