Before You Buy a Home on Septic in Washington: 5 Things You Must Know
Buying a home on septic in Washington State raises a lot of questions, and it’s one of the most common topics we get asked about by buyers considering acreage or rural property.
Septic systems aren’t something to be afraid of, but they are something you need to understand before you write an offer. The rules can vary by county, and a few small details can turn into big, expensive surprises if no one explains them upfront.
Here are the five most important things every Washington buyer should know before purchasing a home on septic.
1. A Septic Inspection Is Not the Same as a Home Inspection
One of the biggest points of confusion is that a septic inspection and a home inspection are two completely different inspections, done by two different professionals.
The home inspection is ordered and paid for by the buyer.
The septic inspection is typically ordered and paid for by the seller.
They are also two separate contingencies in a Washington real estate contract. A standard home inspection does not evaluate the septic system.
If you’re buying a home on septic, you should always make sure there is a specific septic contingency in place.
2. In Washington, the Seller Pays for the Septic Inspection and Pumping
In most Washington transactions, the seller is responsible for paying for both the septic inspection and the pumping.
In counties like Snohomish and King County, the septic system must be inspected and pumped within 12 months of closing.
This protects buyers by ensuring:
The system is currently working
The county has a recent record on file
You’re not inheriting an unknown problem
This is one of the most important protections buyers have when purchasing a septic property.
3. Buyers Should Attend the Septic Inspection
As a buyer, you have the right to attend the septic inspection, and we highly recommend that you do.
This is often the best opportunity to:
Learn how your system works
Understand how the alarm functions
Ask how often it should be pumped
See where the tanks and drain field are located
A good septic professional will walk you through the entire system so you know exactly what you’re buying and how to maintain it properly.
4. Review the As-Built and Know Where the Drain Field Is
Every septic system should have what’s called an as-built on file with the county health department.
This shows the layout of the system, including:
Tank locations
Drain field location
General system design
For older homes, these as-builts are sometimes outdated or even hand-drawn. What matters most is knowing where the system is located.
This becomes especially important if you plan to:
Build a shop
Add an ADU
Install a shed
Subdivide in the future
You cannot build on top of a drain field, and disturbing it can create major problems. Knowing this layout upfront protects your future plans.
5. Septic Systems Are Sized by Bedrooms Not Bathrooms
One of the most misunderstood rules is how septic systems are sized.
Septic systems are designed based on the number of bedrooms, not the number of bathrooms.
This means:
A home designed with a two-bedroom septic can only legally be listed as a two-bedroom home
A three-bedroom home with a two-bedroom septic requires extra due diligence
This doesn’t automatically mean it’s a deal breaker.
But it does mean you should carefully review:
The tank size
The drain field capacity
Whether the system matches your household needs
In some cases, bringing in a septic designer for a second opinion is a smart move.
Final Advice for Buyers Considering Septic Homes
Buying a home on septic in Washington doesn’t have to be risky, as long as you understand the process and review the right documents.
Always make sure you:
Use a septic contingency
Review the inspection carefully
Examine the as-built
Understand how the system is sized
Work with an agent who knows local septic rules
These small steps can save you from major surprises later.
If you’re thinking about buying or selling in Snohomish County or King County and have questions about septic properties, we’re always happy to help.