I'm Winston, a process engineer working in water and wastewater treatment.

Most of my work is sizing the equipment that plants are built from — pumps and pipework, clarifiers and DAF, media and carbon filters, membranes, ion exchange, UV and neutralisation and more.

This started as my own set of calculation sheets. Every engineer builds them eventually, usually in a spreadsheet nobody else can follow, and rebuilds them at the next job. I decided to organise mine properly instead: every equation visible, every result checked against the design envelope industry practice actually accepts, and the working shown so it can be argued with.

The design sheets on winstonwaterengineering.com are free and will stay free. The workbook is the same calculations in Excel, for people who'd rather work in a file than a browser.

Both are still being built. I add to the site as the work throws up something worth adding — new unit operations, new sheets, better tools around the ones already there. It gets updated regularly, and it stays free as it grows.

The workbook follows the site. Every so often it gets a new revision with whatever has been added since, and if you have bought it, that revision is free — Payhip emails you the new file. Buy version 1.0 and you own every version after it.

The site stays free because the workbook pays for it. Buying it covers the hosting and the hours, and it is the reason there is a next sheet. If the free ones have saved you an afternoon, that is the way to keep them coming.

If something here is wrong, tell me — corrections get fixed and credited. If you're stuck on a sizing problem, ask.