Assalamu aleikum
 
In risalat there are simple terms on man:
 
Semen, mani is najes (however if left inside of wife it does not cause her impurity).
Janabah state for man is easy to understand.
 
As for women:
 

1. Hayd blood is najes, hayd explained in risalat.
2. Usual discharge without blood is tahir.
3. Water that appears because of arousal – basically tahir? but in case of orgasm? it is still tahir?
4. Experienced couples may practice what is called – squirt. It is fluid expelled with force from urinary tract. Scientific studies show that it contains urea – so it is – najes. 

 
A French gynecologist, Samuel Salama, conducted one of the most comprehensive studies by using ultrasounds to track the bladder before and after squirting. His findings showed that the bladder fills during arousal and empties once the squirt happens, with chemicals commonly found in urine showing up in the fluid.
 

1. In 1880, Dr. Skene wrote of paraurethral glands (on either side) of the female urethra. 

 
Female ejaculation is thick whitish and milky approx. volume ~ 1 ml.
 

This fluid contains substances similar to male prostate secretions such as prostate-specific antigen (PSA) and has a composition different from urine. It is usually expelled with rhythmic muscular contractions and in smaller volumes, generally a few ml or less.
 
So it is tahir? 
 
My question is not on the janabah (I remember that janabah occurs just because of penetration, however little), but on the purity of various fluids in women.
 
And for me it is now a common sense that Muslim couple must have waterproof blanket(s), just to avoid confusion and keep to laws of purity. And specifically equip the bathroom.