Bedrooms can be counted in 3 ways:
Part of the tax assessment of each house is a count of the number of bedrooms and that number can be found on the field card in the Town Assessor's office.
Every house has some number of rooms that are actually being used as bedrooms.
Septic system design for individual houses is based, as per the Public Health Code, on the number of bedrooms in the house (note: the number of bathrooms is not a consideration). A bedroom is a space that provides privacy (meaning it has a door and it does not provide sole access to other parts of the house), and has reasonable access to a full bathroom. Closets or their absence is not a consideration.
In an ideal world these three numbers would all correlate and in newer houses the system works pretty well. In older houses the numbers often diverge and real estate agents have to come up with a listing that makes sense of the conflicting numbers.
Public Works Records
Microfilm in the Public Works office has some septic system information on most houses, but it is often incomplete and may or may not be helpful in the listing process. In many cases it is not possible to say that house "X" has a septic system for "Y" number of bedrooms. Agents often assume that a 1000 gallon tank indicates a 3 bedroom system and a 1,250-gallon tank indicates a four bedroom system and that would be true for a new house. However, past additions of bedrooms would not have required septic system upgrades, so there are legitimate reasons the Assessors bedroom count might not agree with the size of the system.
It should also be remembered that the size of the tank, which is the part of the system we usually do know about, is far less important to the operation of a system than the size and age of the leaching system as well as the soil conditions in the leaching area. This information may or may not be available on microfilm and in most cases the older the information, the less reliable it is.
All of this leaves buyers, sellers and agents with an imperfect system that provides no definitive way to produce the simple unambiguous number all parties would prefer. As a general rule, it would be wise for all parties to expect increasing problems with increasing time since system installation. It would also be wise to anticipate more expensive repairs in low-lying areas - areas in close proximity and elevation to wet or swampy areas.