Buying a house with a mound system

[Marc Jennings]

I recently bought a house, constructed completed in 2019, sellers listed the home in November of 2019 after living in it for approximately 6 months.  The house utilizes a mound septic and well system as it is located in a country setting.  The house is clearly a four bedroom house and has been from the start of construction, however, when construction was done, the size of the mound was permitted and installed use in a three bedroom house.  When the sellers placed the house for sale through a realtor it was listed and marketed as a four bedroom home.  We have since incurred expenses to increase the size of the mound to accommodate the size of house and water usage for our family.  Is it legal to list and market as a four bedroom home when a three bedroom mound system is installed.  I have been looking at the real estate laws in Wisconsin and have not been able to find anything specific in the statutes.  Any advice would be appreciated.