De or het waterspoeling?

The correct Dutch article is:

de waterspoeling

Rule Words ending in -ing: almost always de. See the rule

How to use waterspoeling

the waterspoelingde waterspoeling
this waterspoelingdeze waterspoeling
that waterspoelingdie waterspoeling
our waterspoelingonze waterspoeling
your waterspoelingjouw waterspoeling
every waterspoelingelke waterspoeling
which waterspoeling?welke waterspoeling?
a big waterspoeling / the big waterspoelingeen grote waterspoeling, de grote waterspoeling