Keith, I can understand your concern that water laying under the home has some potential for damage.
There is a lot of misunderstanding about this, so I am providing some background to illustrate and cover your doubts and the answer further down - ignore the water.
However, the situation is that many homes and other buildings are built over water, Venice for one, and most of Holland and a lot of London etc:
In the UK there are place like Weybridge where the water is just below the grass and many others built on flood plains and in other types of basin where water is slow to get away.
I wonder what the local council planing minutes recorded when your home was proposed and how they managed to ignore the recommendations from the Environment Agency and who made a lot of money from the development?
Until recently the accepted idea was that homes in the UK were badly built, were not water tight and needed a lot of air circulation to continually dry them out after bad weather.
More recently there has been a move towards making homes air tight, indeed all homes built from 2016 will have to be airtight (if our hopeless builders can manage it) to the European Passive House standard and forced controlled ventilation will be required.
From the above you will note that the idea of lots of air circulating under and through a home have been discredited and it has been realized that humid air arriving in or under a home is the problem not the solution.
So forget extra air bricks.
The problem they have in the USA is millions of homes in twelve States suffering from damp and mould, usually due to bad design and building.
Compounded by their weather.
Here the weather is kinder and we do not have such violent swings from very cold to warm and wet.
It is the sudden influx of (in comparison to the existing temperature under a home normally about 12 degrees C) warm wet air under a home that causes mould and sometimes wood rot.
The interesting thing is that warm wet air always makes a bee line for a cold surface, where the air being cooled looses its ability to hold the moisture and the surface becomes wet, mould forms and is sometimes followed by wood rot.
This change of temperature happens about 200 times a year when you see frost or heavy dew.
Where the temperature of the wooden joists and floors under a home is raised by heat leaking downwards by conduction and radiation from the rooms above, these items do not attract warm air, moisture is not deposited and mould does not form.
So to answer your question, water under a home is not a problem as long as it remains below the damp proof course and it is not touching any of the joists or other items that may absorbe water and transfer it to the wood work above.
In fact the water being at the same temperature as the ground it is laying on 12C approx. will remain cold and will atract any warm air or moisture entering the crawl space.
For the sake of your heating bill, go over the floors and try and block all holes however small.
The warm air in your home will rise and disappear out of holes in the ceilings and walls, open doors and windows, air vents, etc; sucking cool air from the crawl space, this air will then be replaced with air from the outside that may be warm and damp. Anything that prevents this air movement is good.
