You are now about to learn one of the most fascinating Dutch grammar rules: The rule regarding the connecting elements -s. Quite frankly, it is hardly worth the qualification 'rule':
we use the connecting -s in written language,
if it is also used in spoken language
This is the official guideline. Even Dutch native speakers, this is far from evident. Since there is not always a 100% agreement among the more than 20 million Dutch speakers about the presence of the connecting s, some compound words can be written both with and without an s. This is the consequence of basing a linguistic rule on spoken language.
Although the use of the connecting -s seems quite random, there are a few nouns that always take a connecting -s when they consitute the first part of a compound noun:
- Verb-based nouns that end in unstressed -ing
| de verdediging + de linie
| de verdedigingslinie
| the defense line
|
| de betaling + het verkeer
| het betalingsverkeer
| the ' payment traffic'
|
| de begroting + het tekort
| het begrotingstekort
| the budget deficit
|
- Verb-based nouns that end in unstressed -er. Many of the non-verb based nouns ending in unstressed -er also use the connecting -s.
| de arbeider + de partij
| de arbeiderspartij
| the labour (workers) party
|
| de beginner + het geluk
| het beginnersgeluk
| the beginner's luck
|
| de ondernemer + de zin
| de ondernemerszin
| the entrepreneurial spirit
|
| het meisje + de kleding
| de meisjeskleding
| the girls clothes
|
| het pakje + de avond
| (de) pakjesavond
| St. Nicholas Eve (Dutch holiday)
|
| het sprookje + het bos
| het sprookjesbos
| the fairy tale woods
|
A few tips
I repeat my advice: Use a spellchecker! Now suppose your compound noun is not mentioned in the dictionary. In this case, the Nederlandse Taalunie has a few tips for you:
- Check your dictionary for a compound noun that begins with the same word. If a connecting -s is used for this word, then you should also use it for your unlisted compound noun. If the connecting -s is not used, then you should not use it either.
- Things will get really confusing if you find several mentionings of compound nouns that begin with the same word as your compound noun, but some of them with and some of them without a connecting -s. If this is the case, use the most frequently mentioned form. In other words, use a connecting -s if most compound nouns in the dictionary that begin with the same word get a connecting -s.
- Check the internet for the most frequently used form.
- Use your 'taalgevoel', your language intuition (certainly most helpful).
De Nederlandse Taalunie is the official Dutch language authority to be found online at 
www.taalunieversum.org.
Questions? 
