On land with no public sewer, whether you can build depends on whether the soil can support a septic system, and the only way to know is a percolation test or soil evaluation performed before you're committed to the purchase, not after. A lot that can't perc, or can only support a small system, can be unbuildable or far more expensive to build on than the listing implies.
A percolation test (or, in many jurisdictions now, a more thorough soil evaluation involving test pits) measures how fast the soil absorbs water and looks at the soil profile: depth to a seasonal high water table, depth to bedrock or another restrictive layer, and slope. Those results, combined with the design flow you need (set from planned bedroom count), determine whether a conventional system fits, whether you need a more expensive alternative design (mound, aerobic treatment unit, sand filter), or whether the lot can't support a system at all.
The test should happen, and results should be in hand, before your due-diligence period ends, with the purchase contract contingent on a passing result (or on results you're willing to build around). Buying raw land first and testing after closing removes your only real leverage: once you own the lot, a failed or marginal perc result is your problem, not the seller's.
If the county already has permit or soil-evaluation history for the parcel or nearby lots, that's a useful starting signal, though it's not a substitute for testing your specific lot; soil conditions can vary significantly within short distances.
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It can mean the lot can't support a conventional septic system. Depending on the soil and jurisdiction, an alternative design (mound system, aerobic treatment unit, sand filter) may still work at greater cost, or the lot may not be buildable for the use you intended without a public sewer connection.
Before you're committed, ideally as a contingency in the purchase contract, not after closing when a bad result becomes entirely your problem.
It tells you what the soil can support for wastewater disposal. The size of house you can build, tied to bedroom count and design flow, follows from that result, not the other way around.
Reviewed 2026-08-31 against the official sources linked above (where a source is cited) or, where none is cited, left deliberately general. Laws, lender overlays and local ordinances change; confirm current requirements with the county or state agency, your lender, and a licensed inspector before you rely on this for a closing.