Dissolved oxygen and tea water

Growing up, my grandmother frequently asked me to gather spring water in the coldest month each year. Replying to my complains, she told me that gathered in this way the water would taste good and stay fresh for a long time. The desolated mountain road was often covered in snow with very few people in sight. Occasionally fallen branches even blocked the road. I always hesitated filling the bottles as the icy cold spring water stung my hands as I touched it. Once I made up my mind, I got out of the heated car, and while shivering, filled up the bottles quickly retreating back to the car. Nobody really knew the science of this good water, but many rural dwellers intuitively understood the water’s quality, as this was common sense.

Sen Rikyu who established Japanese tea ceremony even mentions the importance of quality in tea water. Spring water is the best source of water for preparing tea. Stream water is second and still water such as lake and well water is the least suitable.

The water source has a direct correlation to how much oxygen is available in the water. Oxygen generally makes water taste good and brew better tea. The source of water that contains the highest levels of oxygen are often found in high mountain creeks and fast moving water.

Oxygen typically enters water when air comes in contact with water. Oxygen gets added with aeration which is caused by rapids, waterfalls, ground water discharge and photosynthesis of aquatic plants. Waterfalls and mountain creeks go through lots of aeration and are typically high in dissolved oxygen (DO). Low temperatures of mountain creeks and spring water also tend to hold more DO than high temperature water. This validates my grandmother’s teaching about the coldest time of winter being the best time to fill up spring water.

What affects the level of Dissolved Oxygen?

• Water Temperature – Cold water holds more DO than warm water.
• Low Elevation – Lower elevation holds more DO than higher elevation.
• Turbulence – Fast-moving water generally holds more DO than still water.
• Hour – In the afternoon DO level is usually higher than morning because aquatic plants have released oxygen through photosynthesis during the day. More O2 is removed through respiration at night.

How do you find a good source of water?

The best way is to observe and learn from nature. Measuring dissolved oxygen (DO) is often performed to assess the health of aquatic environments. Certain species of fish such as trout requires high level of DO (>12mg/L) while lake fish like bluegill, bass and carp can tolerate lower level of DO (3-5mg/L). Bacteria needs yet a lower level (<1mg/L). This indicates that you want to get water from the clean and natural areas where trout and salmon live. Or when in the tropics, visit waterfalls.

Perhaps we can create ideal oxygenated water from aeration. Even though I’m a fisherman at heart, it feels funny to drink the water who’s quality is judged by suitabity for fish. I’m beginning to understand that the moisture in cool mountain air within a dense forest is much different from the (albeit clean and fresh) air that circulates around my house.

Hardness, Flavor, and Source

Today we can buy famous spring water from anywhere around the world. But, do we understand the criteria for choosing the water that makes good tea?

Choose soft or spring water, but not distilled or purified.

At an event in Honolulu, I made a serious mistake of brewing with purified water. If you were there I wouldn’t be surprised to hear that you were as dissatisfied with the flavor of our tea as I was.

Purified water is basically distilled water that goes through an additional purification processes to remove impurities. We brewed tea with it and it didn’t taste right. We doubled the leaf to water ratio, and it still tasted very light. We checked the leaf, equipment and water for anything unusual and found out that we were using purified water. Heading back to the store, we then purchased spring water and the tea came out just fine.

What I learned? It turns out that the purification of water removes the elements that are essential for brewing. As mountain dwellers already know, spring water contains minerals (especially calcium and magnesium) which make the water ‘hard’. Only when water hardness is at appropriate levels the will resulting tea taste good.

Since spring water from different locations contains different levels of minerals, make sure to find a desired level of water hardness that suits you.

For green tea, desirable water hardness or mineral content is typically 50-150mg/L. If a lighter taste is desired, find softer water. Some water bottles show the level of water hardness or mineral content on the label.