A little knowledge

First of all this message is born out of experience and some knowledge of houses and house construction in the UK so may not be fully applicable to other countries and their construction methods and regulations. This is by way of a 'wise after the event' tip to any of you buying an older house in the UK. Firstly I hope that this does not apply to new houses these days, but you never know.
Always check/ask what sort of damp proof membrane/course there is to separate the interior of the house from the ground beneath it. For those of you not in the business or familiar with UK construction techniques, all walls, slabs and anything else in contact with the ground needs a water proof barrier separating the ground or ground touching parts from the above ground parts which includes walls, ground slabs but especially the enclosing structure to the living spaces. There are exceptions to this but you should not need to think about them.
If you look at the outside walls of your house you should be able to see the line of the damp proof course in the external wall which should be a minimum of 6 inches, 150mm, above the external ground level. If you see it in your current house, and not all old houses have it, then move soil etc away if it covers/bridges the dpc. Houses with basements have a much more complex/important issue to deal with but the principles are the same. The reason for this is that water will be sucked up in many materials and defeat the purpose of the dpc. The same thing happens with damage to the damp proof membrane that is laid on or under the concrete floor slab. When water is drawn up it damages and often ruins wall and floor finishes as well as decorations, carpets etc. Then of course resultant mould and dampness is a hazard to our health. We have all heard of rising damp, this is what we are talking about and most of its causes.
Now to the point of this message related to my current experiences of rising damp. When we bought our present home we had a survey done as well as me having a good look round. As an architect I thought I knew a thing or two about this sort of stuff. The dpc in the external wall I could see and that looked conventional and the right distance about the surrounding ground level. I did not ask about the damp proof membrane and as the place was fully carpeted/floor tiled I could not see what sort of floor construction the place was blessed with. I assumed that under carpets was the classic cement/sand screed, and therefore the standard floor construction of screed, on dpm, on concrete slab, on hardcore, etc, the point being, and important point, that the dpm needs to be protected from damage and hence penetration from above and/or below. In the standard case by the slab below and the screed above.
When we chose to replace the carpet in the hall I discovered that the place was, what's the word, cursed, with an unusual and 'doomed to failure' construction. The decorative floor finishes sit directly on a bitumastic compound about 15mm thick. Even worse still the timber base plates to the room partitions appear to be sat on the concrete slab with the bitumastic compound butting up either side with no dpm/dpc beneath. But the continuing risk to the dpm, and real problem inherited from the previous owners, was the damage done to it by nailing gripper rods down round the rooms for the fitted carpets. The bitumastic compound is brittle enough to shatter either as the nail goes in, in the first place, or pull out as a small divot around the nail when it is pulled out. This removal of the gripper rods is necessary if you are going to replace the carpets with laminate, tiles, etc.
Hence the hazard inherent in our place and the potential risk from rising damp. This risk was realised when the water feed pipe that runs under our place failed, water pressure in the soil consequently built up, and by whatever routes the water found its way to the underside of the dpm, through the holes/fractures in it and hence into the covering carpets and other floor finishes. In fact the floor finishes acted like wicks drawing up the moisture even faster than the underlying pressure.
Clearly what happened to us is a bit unusual but a high water table, the property being surrounded by higher ground, local flooding, etc, can also show up as problems when the dpm is damaged. What happened to our water feed pipe is not unique as the use of copper piping, often not properly protected from the corrosive effects of the surrounding soils/cements was always going to have a short life. They use plastics not copper these days because of this. The pipe running under the building also means that any problem with it and you are unable to get to it to inspect, repair, replace. I had a conversation with the water board about the problem when they seemed unable to grasp why I could not dig down to it to have a look. We are waiting, wet floors suffered with, for a replacement feed to be dug/laid round three sides of the property.
Oh and by the way this issue, replacing the pipe, is not in the UK usually covered by your house insurance policy nor the policy offered by your water supply company. We are fortunate in the sense that our buildings insurance have offered us about 40% of the pipe replacement cost, but take note.

Just shows that a little knowledge can still be an inadequate thing.

So, buyer beware, check as best you can what the basics of your proposed house purchase are letting you in for.