Studies show common advice for avoiding UTIs is no benefit.

Increasing fluid intake? avoiding occlusive underwear?

Often websites contain advice regarding how to avoid a UTI, this information is the passed between friends and individuals - even health care professionals. The European Urology Association (EAU) has recently reported on studies investigating if these common interventions actually help. 

The common advice of drinking more fluid as well as wearing loose fitting cotton underwear were shown to have no positive effect. This being said adequate water intake is important for general health and well being, and should not be avoided. The good news is you can choose the underwear you wish to wear. Both actions will not reduce UTI rate. 

Reference: http://www.bpac.org.nz/BT/2015/July/guide.aspx