Walk into most water and wastewater engineering consultancies in 2026 and their calculation tooling looks remarkably similar to what it did in 2006. A shared drive full of spreadsheets, named with some variant of the word "final," each one a mosaic of locked cells, hidden rows, and formula logic that only the original author can reliably navigate. Excel is not a niche workaround in this industry — it is the primary calculation tool for the majority of practising engineers, from graduate level upward.

This is not a criticism of those engineers. Excel solved a real problem at a time when nothing better existed, and in many ways it still solves it. But in 2026, with purpose-built tooling available and accessible, the persistence of the spreadsheet as the default calculation environment deserves some examination.

How Excel became the default

In the 1990s and early 2000s, Excel was genuinely the best accessible tool for engineering calculation work. It sat between manual calculation (slow, no iteration) and bespoke software (expensive, inflexible, often tied to a single vendor). It required no programming knowledge, it was already installed on every office machine, and it produced output that looked like a calculation sheet, something that clients, checkers, and PI insurers understood.

Engineers adopted it naturally. Firms built up libraries of spreadsheets: one for pipe sizing, one for pump selection, one for hydraulic testing, one for chlorine dosing. Those spreadsheets got passed around, slightly modified, and passed around again. Over time they became institutional assets, trusted not because they were rigorously validated, but because they had been used without obvious error often enough that nobody questioned them.

Why it is still the default in 2026

The short answer is inertia, but that is not the whole story. There are genuine reasons why firms have not moved away from Excel, and dismissing them makes it harder to understand what better tooling actually needs to offer.

Familiarity. A senior engineer who has used the same pipe sizing spreadsheet for fifteen years knows exactly where the inputs go, what the outputs mean, and how to sanity-check the result. Asking them to switch to an unfamiliar tool introduces friction and, in their mind, new risk.

Checking culture. Water infrastructure calculations are typically checked and approved by a second engineer. The checker knows how to open a spreadsheet and trace a formula. A black-box web tool, in their view, offers less visibility into the working, even if the method is identical.

Flexibility. Excel can be shaped into almost anything. A bespoke calculation that doesn't fit any standard template can be built in an afternoon. Purpose-built tools by definition cover defined scope.

No compelling alternative. Until recently, the options were either expensive licensed software (Infoworks, WaterGEMS, EPANET for network modelling, all appropriate for different problems but heavy-weight and not suited to day-to-day back-of-envelope design calculations) or nothing at all.

The hidden risks of spreadsheet calculations

The problem with Excel is not that engineers use it badly. It is that Excel makes certain categories of error structurally easy to make and structurally hard to catch.

A 2013 study by Panko found that approximately 88% of spreadsheets contain errors, with roughly 1% of all formula cells containing mistakes. In engineering calculations where a single formula drives multiple dependent outputs, one wrong cell reference can silently corrupt an entire sheet.

Cell reference errors. Copy a formula one column to the right and a relative reference silently shifts. This is the most common and most dangerous spreadsheet error in engineering work. Invisible in normal use, potentially significant in output.

No unit checking. Excel has no concept of physical units. A flow rate in litres per second and a flow rate in cubic metres per second are both just numbers. Mixing them produces a number that looks plausible and is wrong. The engineer has to track units manually throughout.

Version control. Spreadsheets are typically managed by email and shared drives. "FINAL_v3_revised_FINAL.xlsx" is not a joke; it is a genuine description of how calculation files accumulate in practice. There is no reliable way to know which version of a spreadsheet was used for a specific design decision made two years ago.

Undocumented assumptions. The inputs and constants buried in a spreadsheet often carry assumptions that were reasonable at the time of writing and become invisible over years of reuse. A roughness coefficient set for new ductile iron in 2010 may be silently applied to an aged cast iron main in 2026 because nobody thought to check.

Institutional knowledge lock-in. Complex firm spreadsheets are often understood in full by one person. When that person leaves, the spreadsheet becomes a trusted black box, used but not understood, which is the worst possible state for a calculation tool to be in.

What has changed

The technical barrier to better tooling has effectively disappeared. Modern web technology makes it straightforward to build calculation tools that are fast, accessible from any device, methodologically transparent, and consistent in output. The cost of building and hosting them is a fraction of what bespoke engineering software cost in the 2000s.

What has not changed is the cultural and institutional inertia described above. Tools that want to replace Excel in day-to-day engineering work need to clear a higher bar than simply being correct. They need to be trustworthy in a way that an engineer with PI liability can accept. That means showing their working, citing the standards they implement, and making it easy for a checker to verify what the tool did and why.

The sign-off requirement does not go away. Better tooling does not mean removing the engineer's judgement from the process. It means giving engineers cleaner, more reliable inputs to apply that judgement to. Every calculation output still requires review and sign-off by a practising engineer before it is used in a design.

What better tooling looks like

The shift away from Excel does not require a wholesale replacement of every firm tool overnight. It starts with the most routine, repeated calculations: the ones done dozens of times per project, where the method is settled and the value is in speed and consistency rather than flexibility.

Pipe sizing is a good example. The method is standard. The inputs are straightforward. The output is a nominal diameter. Doing this in Excel takes several minutes, requires the engineer to maintain their own velocity limit table, and produces a file that needs to be named, saved, and version-controlled. A purpose-built tool does it in seconds, applies the correct velocity limits for the fluid type automatically, and produces a result that is the same every time.

What that shift requires from a tool is not just correctness but transparency: show the method, cite the source, surface the intermediate values so a checker can follow the working without needing access to a formula bar. That is the standard Excel is implicitly held to, and it is the standard purpose-built tools need to meet before they will be trusted as a replacement.

The industry is not going to abandon spreadsheets overnight. But the conditions that made Excel the only viable option no longer exist. The question for 2026 is not whether better tooling is possible (it demonstrably is) but whether firms and engineers are willing to change the habit that has been the path of least resistance for thirty years.