New Hampshire Septic approval: what it allows on a lot
Septic approval is New Hampshire law, and the official source is at des.nh.gov.
A new or replaced septic system needs state subsurface approval from NHDES.
Whether it applies to one lot turns on where the lot is and what it is zoned; the city, county or state office named in the law decides. Mapped areas are approximate. This is a plain reading of public law with its source, not legal advice.
Free, no account. ParcelSheet shows the lot's mapped size, parcel lines and flood zone, and this law on the lot's New Hampshire sheet.
Other New Hampshire laws on a lot: Accessory dwellings (RSA 674:71), HB 1079 (2026), in force August 31, 2026.