That basement stain keeps coming back. Look uphill for where the water gets in.

Take both to the basement and answer the four questions on the card. Which wall faces uphill, in which months it turns damp, whether it is bare masonry or a finished wall, and what runs under your street.

Give the notes to whoever you book. An assessor who starts from your answers can skip the guessing and go straight to the likely entry point. If you are not sure about an answer, say so. A guess written down as fact sends the survey the wrong way.

If your wall turns damp in late winter and spring, soil water is a likely cause. Essex County's hazard plan puts the highest water tables in late winter and early spring.

If the wall only turns damp in July and August, humid air is a likely cause. Newark's climate normals put the dew point at 60 degrees or higher for nearly every hour of those two months. A cold masonry wall can then collect moisture with no leak at all.

Either way, tell the assessor the months. It changes where they look first, and it keeps you from paying to chase the wrong cause.

• Uphill-First Moisture and Mold Assessment finds the entry point and writes down what is wet, what is moldy and why. Book it before anything is torn out.
• Mold Remediation to the Written Plan removes what the survey found. Ask who confirms the result afterward.
• Water Damage and Wet Basement Drying dries the structure and closes the path the water took. Fresh leaks may need it first.

We are not any of the three companies. We help you book the assessment and tell you what to ask the others.

Start with the survey. An assessor who will not do the removal has no reason to look anywhere but where the water enters. Then a separate company removes what the survey found, working from the written plan. Last, someone dries the area and closes the route the water took.

If a contractor already quoted a tear-out, ask what showed them where the water gets in. A removal price given before a survey is a guess.

When the water is a fresh leak, drying can come first. The EPA says quick action in the first 24 to 48 hours can head off mold growth. If your wall got wet this week, call before you read further.

No state body certifies mold companies, so you arrange the separation yourself. Booking the assessment first is how you arrange it.

Montclair sits on the slope itself. Glen Ridge runs along the ridge line, and Verona sits between the First and Second Watchung Mountains. Belleville and Nutley run down to near sea level. Clifton, in Passaic County, climbs from sea level to about 415 feet.

Pick your town on the areas page and read how the ground lies there. Then book from that page, so the first question you answer is the one that fits your hill.

The American Community Survey estimates that the typical Montclair house dates to 1938. About 59.4 percent of its homes went up before 1940.

Many of those basements were later finished with studs, insulation and drywall against masonry. The state health department warns that mold can grow unseen in basements and behind walls. If your basement is finished, ask the assessor whether the wall behind the drywall is part of the survey.

If you are buying, P.L.2023 c.93 requires the seller to say whether the home has had flood damage, seepage or pooled water. Read those answers, then ask an assessor what to check before your closing date.

If you rent, your landlord must give you a signed flood rider before you sign or renew. Keep it, and tell us what the wall shows. If your landlord calls the damp just humidity, the months tell you more: see the renter guide.

The company you hire sets its own price. These are the things that move it, so you can ask about each one.

• How far the wet area reaches along the wall.
• Whether finished walls must come out to reach it.
• How many places the water gets in.
• How much containment the work needs.
• How long drying takes before repairs.
• Whether the path the water took is fixed.

Ask each company for a written scope before you agree to anything, and compare scopes before you compare totals. Ask what each visit costs before it starts. If a company wants to start tearing out before anyone has found where the water enters, ask for the survey first.