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."