Choose Your Level: Reduce Water Waste with the right Purity

In a previous Green the Bench post, Stop the Flow: Saving Water with Recirculating Chillers, we explored how you can reduce water use through the use of recirculating chillers. This time, we're focusing on selecting the right purity of water for your use.

We often think of water in the lab as something that simply flows when we turn on a tap. But not all water is the same, and the environmental cost of producing the highest grades of purified water is much higher than most people realise. If we use higher purity water than a task actually needs, we waste precious water for no scientific benefit.

Understanding Water Types in the Lab

In laboratories, we often talk about different water qualities, usually described as tap water, Level 3, Level 2, and Level 1. These correspond to international standards (e.g., Type III, II, and I water) used to classify water purity based on what contaminants have been removed and how.

💧 Tap Water

Untreated mains water, suitable for non-critical tasks like floor cleaning or general wash-down.

3️⃣ Level 3 (Type III)

Basic purified water generated typically via reverse osmosis. Suitable for rinsing glassware, autoclave feed, water baths and other non-critical uses.

2️⃣ Level 2 (Type II) 

General lab DI water with higher purity, used for reagent preparation, buffers and many routine workflows.

1️⃣ Level 1 (Type I) 

Ultrapure water for highly sensitive applications like trace analysis, cell culture, and some spectroscopy that require very low ionic and organic contaminants.

Each increase in purity removes more contaminants, but comes with a higher environmental cost.

Why Higher Purity Water Costs More Than You Think

Most DI systems in laboratories start with reverse osmosis to produce purified water before additional polishing stages (ion exchange, UV, filters) to bring it up to Level 1 or Level 2 quality. What many people don’t realise is that the reverse osmosis stage is inherently wasteful.

For every litre of high-purity water produced, typical reverse osmosis systems discharge around 3–5 L of reject water.

That reject water usually goes straight down the drain.

So when we grab Level 1 water for something that only needs Level 2 or Level 3 quality, we’re not just overshooting what’s scientifically necessary but increasing water demand by up to 5 times.

Where Does the Reject Water Go?

Right now, most laboratory reject water is simply sent to drain. There are very few case studies of labs actually reusing this reject water. However, other sectors (like industrial cooling and healthcare) have examples of reuse of reject water for tasks like cooling water or equipment wash down.

This lack of documented lab examples highlights two things:

• There’s untapped opportunity for labs to evaluate reject water reuse in appropriate, safe ways.

• But equally, reducing unnecessary demand for high-purity water remains one of the most impactful first steps labs can take right now.

Action of the Week

• Educate and label which water taps are delivering Level 1, Level 2, and Level 3 water?

• For each routine task (e.g., rinsing glassware, buffer prep), note the quality of water being used.

• Identify any tasks where higher quality water is being used out of habit, not necessity.

Conclusion: A Step Towards Sustainability

Choosing the right water quality isn’t just about good lab practice, it’s about stewardship. When scientists lead by example in careful resource use, we not only save resources and expenses in our own labs, we help normalise sustainability as a core part of how good science is done.

Let’s work together to ensure that our laboratories are not only efficient but also environmentally friendly. Remember, every small action counts.