When you’re buying a home, the focus naturally falls on location, layout, and price. The building inspection gets booked. The pest inspection gets booked. But one area that consistently slips through the cracks — sometimes with very costly consequences — is the plumbing, gas, and drainage systems.
Unlike a cracked wall or tired carpet, plumbing problems are largely invisible. They live inside walls, under slabs, and underground — and they don’t show themselves until they’ve already caused significant damage. By that point, you’re the owner, and the repair bill is yours.
Here are 10 plumbing, gas, and drainage risks that commonly go undetected in pre-purchase inspections — and why a dedicated inspection is one of the smartest investments you can make before settlement.
01 Hidden Pipe Corrosion
Many older homes were built with galvanised steel or cast iron pipes that look perfectly fine on the outside — but inside, they’re slowly corroding. Over time, this leads to reduced water pressure, discoloured or rust-tinged water, and eventually, sudden pipe failure. Replacing corroded pipes is one of the more significant plumbing costs a homeowner can face, often running into the thousands. A professional plumbing inspection can identify at-risk materials before they become your problem.
02 Tree Root Intrusion in Drainage Lines
Tree roots are naturally drawn to moisture and will find their way into drainage pipes through the smallest crack or joint. Left undetected, they cause progressive blockages, pipe deformation, and eventual collapse — requiring costly excavation and pipe replacement. The trouble is, everything above ground can look completely normal. A CCTV drain inspection is the only reliable way to see what’s happening underground before you sign on the dotted line.
03 Non-Compliant or Unlicensed Gas Work
Not all gas work carried out in a home has been done by a licensed tradesperson — and not all licensed work has been done to code. Previous owners may have had gas lines, appliances, or fittings altered or installed by someone cutting corners. Non-compliant gas work is not just a rectification cost; it’s a safety risk and can void your home insurance. A gas inspection checks every connection, appliance, and line for compliance, so you’re not inheriting someone else’s shortcuts.
04 Slow or Failing Drainage from Blocked Sewer Lines
Partial blockages in the main sewer line don’t always announce themselves dramatically. Toilets flush, sinks drain — just slowly enough that you might not notice during a walk-through. But a partial blockage can quickly become a full one, resulting in sewage backflow into the home. A CCTV drain inspection reveals the true condition of the sewer line, including built-up grease, root intrusion, or cracked pipe sections, well before they become an emergency.
05 Hot Water System Nearing End of Life
Hot water units have a typical lifespan of 8 to 12 years. A system that’s technically functioning on the day of inspection may be well past its expected service life — and replacement can cost anywhere from $1,500 to $4,000 or more, depending on the system type. Standard building inspections don’t always flag ageing hot water units. A dedicated plumbing inspection will assess the system’s age, condition, and compliance, giving you a clear picture of what’s ahead.
06 High Water Pressure and Failing Pressure-Limiting Valves
Excessively high water pressure is one of the most overlooked issues in home plumbing. You can’t see it, and it rarely causes a dramatic failure — instead, it quietly stresses every pipe, fitting, and appliance in the home over time. It also points to a potential issue with the pressure-limiting valve (PLV), which regulates incoming water pressure from the street. A faulty PLV is a relatively inexpensive fix when caught early, but the downstream damage it causes to tapware, hot water systems, and dishwashers is not.
07 Deteriorating or Incorrectly Joined Pipe Materials
Homes built between the 1970s and 1990s may contain polybutylene pipes — a material that was widely used for a period before its tendency to crack and fail became well understood. Other homes have a mix of pipe materials that have been joined incorrectly over the years, creating weak points at every junction. These issues are inside walls and under floors, completely invisible without a proper inspection. Identifying them early can prevent water damage that runs into tens of thousands of dollars.
08 Stormwater and Subfloor Drainage Problems
Poor stormwater management or blocked subfloor drainage is an issue that often only reveals itself after the first heavy rain following settlement. Water that has nowhere to go finds its way under the home, creating rising damp, timber rot, and — in serious cases — foundational issues. Stormwater and subfloor drainage systems are rarely assessed in a standard building inspection, making a dedicated drainage check an important part of any thorough pre-purchase due diligence.
09 Leaking or Incorrectly Installed Gas Appliances
Gas appliances — cooktops, heaters, hot water systems — can develop slow leaks at their connections over time, particularly if they were improperly installed or haven’t been serviced. A slow gas leak is not something you’re likely to detect during a home viewing. It requires a pressure test and a thorough inspection of all appliances and connections by a licensed gas fitter. Without one, you’re relying entirely on the previous owner’s word that everything is in order.
10 Hidden Water Leaks Behind Walls or Under Slabs
Slow internal leaks — behind wall cavities, under concrete slabs, or beneath flooring — can go undetected for years while causing mould growth, timber damage, and structural deterioration. By the time visible symptoms appear, the remediation cost is often far higher than it would have been had the leak been caught early. Pressure testing as part of a professional plumbing inspection is one of the most effective ways to identify these hidden leaks before they become the new owner’s headache.
Don’t Buy Blind.
A dedicated plumbing, gas, and drainage inspection gives you a complete picture of the property’s systems before you commit. It’s not just about peace of mind — it’s about knowing exactly what you’re buying, and having the information you need to negotiate, plan, or walk away.
