If you are buying a home with a private well it would be a big mistake to not test your well water for Coliform and E-coli bacteria. It might be the single most important thing you do before buying your home. The NYS Dept. of Health recommends testing private water wells for bacteria annually. Various municipalities and counties suggest and even require by law additional well water analysis, check with your realtor or the local health authorities as to what may be recommended or required. For instance: Westchester County Law requires elaborate comprehensive well water analysis for approx. 75 items performed BEFORE the deed changes hands – this analysis can be quite expensive and is typically done by the seller before even putting the house on the market.