If you are on the pill and taking it accurately, you are not engaging in unprotected intercourse. However, you can always consider taking a pregnancy test. The over the counter tests are quite accurate.
The "theory" behind water ionizers is that they are supposed to make water "alkaline" and, if you drink enough water, your body is supposed to suddenly turn alkaline which, supposedly, makes you more healthy, cures all illness, blah, blah, blah.
This theory is, frankly, the south end of a horse going north.
Different fluids in our body have different pH levels and this is NORMAL. For example, the normal pH of the stomach is highly acidic (pretty close to battery acid for that matter); this allows us to begin the process of breaking down the protein we consume into amino acids; without this breakdown the small intestine wouldn't be able to absorb the protein we eat.
Drinking alkaline water will NOT cure cancer. Trust me; I'm a survivor of breast cancer and if this stuff worked, I'd be guzzling it down.
This has nothing to do with a hysterectomy that happened 15 years ago, much as one poster likes to blame everything on this surgery.
At 51 you may be entering menopause naturally and with this can come vaginal dryness. This can sometimes causing bleeding after intercourse. Other more serious medical issues can also cause abnormal vaginal bleeding. Best to get this looked into medically.