John Mac, PE

From site assistant to licensed engineer

I started on residential water tank installations in 2011 as a site assistant. Two years of field work showed me how often tanks were undersized, set too low for decent pressure, or loaded onto roofs that were never checked. That pushed me into engineering.

• 2011Started as a site assistant on residential water tank installations.
• 2013Completed a BS in Civil Engineering with a focus on hydraulics.
• 2016Licensed as a Professional Engineer (PE) in Texas. Began working full-time on home and small commercial water storage systems.
• 2016–presentMore than 180 residential tank projects covering tank sizing, rooftop structural loading, pressure and float-valve problems, overflow and sediment, and treatment of well water containing iron and manganese.
• 2026Joined WaterTankCalculator.com as author of the site's calculators and guides.

Every calculator and guide on this site

John is the author of all 75 calculators and the water guides on WaterTankCalculator.com. Each category below links to its tools, with a note on where his field work applies.

• Volume & Capacity12 calculatorsRectangular, circular, horizontal, cone-bottom and other tank shapesWrong capacity was one of the most common problems I saw on site: tanks sized from labels or external dimensions instead of real internal volume.
• Household Sizing6 calculatorsTank size for homes, apartments, schools and commercial buildingsSizing homes and small commercial buildings has been the core of my work since 2016.
• Flow, Refill & Time6 calculatorsRefill time, drainage time, pipe flow and meter readingsFloat-valve and refill problems usually come down to a flow rate nobody checked.
• Weight & Structural Load5 calculatorsFull tank weight and rooftop load checksRooftop structural loading is a big part of my engineering work — a full 1,000 L tank weighs over a tonne.
• Pressure & Height6 calculatorsGravity-fed pressure, pump head and shower pressureLow pressure from a tank set too low is a mistake that's cheap to avoid and expensive to fix.
• Water Treatment10 calculatorsChlorine, bleach, pH, hardness and disinfectionI've treated well water for iron and manganese, and I check every dose on these tools against EPA and WHO guidance.
• Rainwater Harvesting7 calculatorsCatchment, first-flush sizing and payback
• Agriculture & Irrigation9 calculatorsCrop, livestock, drip and greenhouse water needs
• Cost & Comparison8 calculatorsTank, installation and supply cost comparisons
• Emergency & Survival6 calculatorsEmergency storage, stockpile duration and disaster prepEmergency figures on these tools follow CDC and FEMA guidance: at least 1 gallon per person per day.

How I check a calculator before it goes live

1. Work the math by handI run each formula with known values and compare the tool's output against it. Reference tables on the page are recalculated from the same formula, so the table and the tool always agree.
2. Set realistic defaultsDefault values — bleach strength, daily water use, alkalinity, pressure limits — come from current published guidance and what I actually see on real systems, not rounded guesses.
3. Trace every claim to its sourceIf a page says "EPA recommends" or "CDC advises", that figure is checked against the agency's own publication. If I can't find it, it comes off the page.
4. Add the safety limitsAnything that touches drinking water or structural load gets clear limits: contact times, when water is not safe to drink, when a roof needs an engineer's check.
5. Date the reviewEach tool shows who reviewed it and when. When guidance changes, the page is reviewed again and re-dated.

Sources I rely on

I use primary sources wherever they exist and cite them on each tool.

My role on this site

I write and review the calculators and practical guides on WaterTankCalculator.com — tank sizing, pressure, roof loading, flow, overflow, sediment, hardness and basic chemical treatment. Alongside this site I continue independent consulting on residential water storage systems.

Spotted an error? Let us know through the About page. I review every report, and corrected pages show the new review date.