I worked in cable for 10 years..Kevins statement (above) is a common problem. If you have cable internet you have a bad fitting, splitter, splitter configuration or a bad line somewhere. If you don't know how to correct these issues, you will need to have a technician test the lines with his meter to test for SNR (signal to noise) and RF levels.
To explain the water issue further, water can get into outside hardware if you get lots of rain or snow. The outside fittings of coax cables should be greased and properly tightened. With an overhead infrastructure (lines off the poles) water can get into the taps (fixtures you share with your neighbor at the telephone poles) .
Underground systems only get water if it gets in the ground block at the house or the pedistal is submerged or flooded- (Pedistal is a box in the rear easement of your yard)
Outside fittings should have electrode grease and some may have rubber boots, but grease is best to keep water out.
However from my experience the most common problem I have seen is that the customer would have a self installed splitter configuration inside their house, in attempt to add more TV's. Also the majority of the time, I see junk hardware installed that is sold at Menards, Walmart, ect. If not installed correctly, or they have bad hardware can cause noise in the line, also take signal away from your internet line. The internet suffers or goes out intermittently if there is too much noise in the line. Fittings aren't as simple as it looks, I have even seen most electricians try to make fittings and most of them were bad.
All splitters have a mhz value. two way splitters have two 3.5 legs, 3 way splitters will have either two 7.5 and a 3.5 leg or three 5.5 mhz legs. and a 4 way spliter has four 7.5 hz legs.
You can get an eight way but it really eats up signal, therefore you'd need an amplifier..thats another subject though!
