A water tight roof and leak free gutters will direct water away from your walls and into the sewer system, causing you no problems to your property, and keeping everything inside nice and dry,providing your drains are free of cracks,(more on that later).
Put a bucket under a dripping tap,you'll be shocked how much water collects in 24 hours.
1)Roof:Old pointing(cement),that's starting to break down in your gullies , your gable ends and between your ridge tiles will allow water to penetrate your roof,usually its not spotted and water penetrates for years,causing your roof timbers to start to rot,if ignored will eventually cost you a new roof.
2)Gutters:Leaking gutters will cause a whole new set of problems,a wet patch on your walls or a hole on the ground ,if they've been leaking for years and water running down your walls will wash the cement out of the joints ,and sometimes cause the faces of the bricks to be blown off.
Over time water will permeate through your brickwork and into your house,and this will cause damp,mould spores to grow and mould is hazardous to your health. A young actress and her partner died 2 Christmas's ago,this was said to be caused by mould growing in their Beverly Hills mansion.
If this happens ,you'll have to have the plaster removed in affected areas and re plastered,and room re decorated,(not cheap for a small cheap to sort drip).http:/www.nice-n-white.co.uk