Most silver procedures do specify de-ionized water, also if you take tap 
water and place some silver (methenamine ) in it you will see a milky 
consistency appear, sometimes visuals pay off.Also if you are using 
positively charged slides, tap water negates the charge on the slide. 
Manufacturers may be able to give you documentation to that effect. Thirdly 
contact your local water company and they can give you a counting of 
coloforms(yucky gram pos and Gram neg counts), and elicit your pathologists 
assistance with all this in hand.
Good Luck.                                         Dana Dittus
                                                          Histology Supervisor
                                                           Abington Memorial 
Hospital