Before buying or selling a home it's a good idea to check the drainage. Master Plumbers, Gasfitters and Drainlayers NZ deputy chairman Dave Strong says members are often asked to do home inspection plumbing and drainage reports.

Homes sell better in the summer. You are more likely to see drainage issues in the winter, however, when rain can uncover all sorts of problems. That can include leaks, leaving a home feeling and smelling damp, or boggy ground that isn't draining properly.

The most common issue is soak holes that have reached their use-by date, causing blocked stormwater lines or wastewater drains, says Strong.

If the work involves re-routing the stormwater into standard 60sq m soak holes in the garden, it will usually cost around $2000, he says.

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Blocked stormwater and wastewater drains may be more problematic. Sellers will often opt to pay for a camera to be put down the offending pipework to determine if there is a problem, which will usually cost around $300.

"The cost for repairs could be $500, $5000 or $10,000, depending on the level of the problem," says Strong. Some blockages can be blasted out with a high pressure hose.

Others may be blocked by roots from trees. Old-fashioned clay drains are especially susceptible to this.

Strong says he sees instances where home owners have connected the stormwater into the wastewater system to bypass a problem.

In the city that means the water is draining into the municipal sewage treatment plant. In rural homes that may cause problems with the septic tank.

Modern homes on slabs tend to be lower to the ground than older homes, says Strong, which sometimes results in problems where the sub-floor drainage has not been properly installed.

There are "good sellers and bad sellers", adds Strong. Good sellers will get a report done and then either fix the problem themselves or at least let buyers know what needs to be done.

Bad sellers, he says, will pick a professional's brain to find out what might need to be done, do a "bodgy job" themselves, and flick the problem on to the next owner.

One of the things for buyers to look out for, says Strong, is new carpet or paint in a low lying area of the home with no other work done elsewhere. This may indicate there has been a problem with rising damp or a flood in the recent past.

It's not uncommon to find both as a result of blocked stormwater drains. If the spouting and downpipes are correctly fitted the stormwater may back up causing problems.

In smaller communities buyers sometimes ask around local plumbers and drainlayers, says Strong, and find out that a home has suffered from a series of wastewater blockages. Drainlayers often received panicked calls at the 11th hour from vendors, says Strong.

If the buyer has concerns, a professional plumbing and drainage report can highlight problems. It can also identify work that isn't up to building code.

Drainage issues can be hard to see with the untrained eye. Strong points out that no specific qualifications are needed to provide home inspection reports to buyers, and most make visual checks only, which may not identify problems that are out of sight.

"They might say: 'The spouting looks fine, it has downpipes that go into the drain'. But they may not even know if it's the right drain. That requires some knowledge," says Strong. "A good (inspector) might have an imaging camera that picks up damp spots. But they don't always."

Sometimes the water ingress may come from surrounding properties. Each council has its own stormwater discharge rules. But typically it is not acceptable for discharges to cause or exacerbate flooding of other people's property.

Householders sometimes oppose consent for neighbours' works on the basis of the work's likelihood to cause damage or nuisance to their property.

Such objections should show up on the LIMs (Land Information Memorandums)and highlight potential flooding/drainage risks to the property.

Buyers need to look out for defective drainage notices, which also show up on the LIM or council file.