One big database or little separate ones?

In creating a database I am trying to determine which method is the better way 
to go. No, I do not know what "better way" means, novice is the key, hence 
this post.

The basic question is, what point(s) are used to determine there are enough 
tables and another database should be created. Hmm, well let me say it this 
way.

Here are briefly (for the most part) the things I want in a database;

1. customers - the usual stuff, names, addresses, etc.
2. well logs - depth of water wells, location (latitude/longitude as well as 
the normal address), layers drilled through, etc.
3. excavator work - hourly rate, length of dig, etc.
3. plumbing - items used on project, part cost, etc
4. septic work - installation of septic tanks, address, cost, etc
5. water softeners - customer name, is it a rental or not
6. supplies/parts - inventory type stuff.

The basic decision here is, do I put all this into one database with a bunch 
of table? Or would it make more sense to separate it out? If there are 
separate databases will it prevent linking tables between the two?


-- 
Registered Linux user 193414
http://counter.li.org

"Trying"? My contribution was much closer to a "feeble wave in the general 
direction of something that might lead you one step closer to a solution 
if you squint really hard and do all of the work."