Sometimes the rain comes faster than the earth can drink it up. Before you know it the sewer system is becoming overwhelmed. Its pretty common place to have a flooded basement or at least some seepage if you have a home that was built before they thought to take measures to water proof the foundation walls before back filling.
Many older homes will start to take on water in their basements, because after all back then, basements were not really intended as a living space more than they were just for storage or utilities. the foundation walls were not water proofed nor were there vapor barriers or water proofing under concrete floor slabs.
Some of the ways water will come in are easy to deal with, but sometimes it can be difficult to diagnose and correct. Obtaining the help of a good Home Inspector can make a big difference.
You have seepage through ground water- as it rains and the water table rises it will find its way through a path of least resistance- say a crack or a gap along the wall - the term for that is hydrostatic pressure. There are companies that can seal cracks with an injected epoxy, but some times the water finds another way in.
Sometimes you will notice that the leaks are more prominent where there are downspouts located on the exterior. If the downspouts are too close to the homes foundation (within 6 feet away) it can mean more dramatic leaking. Bad lot grading can make things even worse, of course.
If you have a large tree close to your homes foundation it may cause large cracks that can let water in, or it can also cause clogging of your pipes (the small capillaries of the trees roots find their way to water through the connections in the piping). That's why it is recommended to have a plumber Rod out your waste pipes and also route a camera inside the length of pipe to look for damage or other problems like offsetting of a pipe connection due to odd settlement of the home for instance. That maintenance should be done once a year to every 2 years.
Another way water can enter is from clogged gutters. This condition may cause water to actually wick up the roof covering and possibly enter the walls. If there is a poorly installed flashing or no drip edge, it will be worse yet. That's when the dreaded mold issues can become prominent ,especially if there is continued dampness of the wood or other cellulose material that feeds molds. Clean those gutter regularly.
There is the possibility that local sewer systems do become overwhelmed and back up. Then there is actual waste water backing into the home- yuk. Not only does it smell but it can be unhealthy to breath the air - let alone coming into contact physically with it. Cleanup can be very unpleasant, and any belongings in the basement will be ruined - not to mention any finished walls that need to be torn out to avoid the possibility that biological substances will proliferate because of the the sewer water soaked insulation or drywall paper or paneling or what not.
WHAT CAN YOU DO ABOUT IT?
( At the very least) Some older homes have what a manual shut off / back flow preventer valve. You do have to be there to crank it shut before the water backs up. So if your not home, its not working. Of course now they make automatic mechanical and other advanced types of flood controls valves. Note: You shouldn't use your homes plumbing when you close the valve or you could flood it your self. Also understand that, if ANY valve is not maintained for a period of time they may not work well when called upon. My own home has a back-flow preventer valve that is damaged because the previous owner had not maintained it properly.
(GOOD) Some homes have a perimeter drain either inside the basement floor or outside of the foundation footing. These work well for seepage but sometimes they can become clogged with silt and become less helpful. Many of the basement "water proofing" companies will install an interior perimeter drain tile system routed to a sump or ejector pump. In addition, they will use one method or another to "seal" the walls and cracks to try to prevent leakage. Sometimes after all that, you still get water. Installing a footing drain is costly, but especially if it is an exterior footing drain tile system. When excavating around the exterior of your home, there is now an opportunity to seal the walls, greatly reducing ingress of water, but it is a pretty big job involving removal and re pouring concrete for side walkways and will not be cheap as it all very labor intensive and heavy machinery will be needed.
(BETTER) Sump pumps can help keep basements dry - but not necessarily in a big storm that knocks the power out - unless there is a battery back up system in place. However- you must have the sump pump discharge routed in such a way that the pumped water will not just seep back in. Its becoming increasingly common for homes to have at least a sump pump if not a ejector pump as well (especially when a basement has a bathroom present.) Always use a battery back up system.
(BEST) The most effective system is installation of a Overhead sewer system. This is a pretty costly system that removes the ability for the street sewer line to back into your home because there is no direct link. Basically, the waste from your home is pumped up and in to the municipal sewer system with the help of gravity. Of course a power outage will stop it from working unless there is a battery back up system present- highly recommended! Always use a dehumidifier during the summer months to reduce condensation moisture problems.
BTW- [glow=red,2,300]Feel free to share your horror stories and what did work and what didn't work. Together we may win this war against wet basements..!
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