Water Leak

• When pipes leak, water marks will appear on painted walls. If there were no water marks on your wall when you painted it but lines appear through the paint some time later, a new leak is likely. Contact a professional before extensive damage occurs.
  
  

Inadequate Preparation

• If you attempted to paint directly over an existing water stain, bleed-through was inevitable if you failed to use a primer. The right primer base coat would have permanently sealed the water marks. Read primer cans carefully or seek a paint specialist's expertise when determining what kind of primer your wall surfaces will need.
  
  

Improper Materials

• Ordinary latex primer will not block water marks. For best results, choose a shellac stain-blocking primer. This will permanently prevent the water marks from bleeding through the painted finish.
  
  

Considerations

• Water mark lines are sometimes the result of flooding. As with other water stains, flooding water marks cannot be cleaned. Prime and paint over the entire wall, using the proper materials, or the stain will eventually bleed through. Depending on the severity of the flooding, you may need to replace your flood-affected wall material as well.