Water Quality

Water Quality image

It also explains the water quality class of the river in terms of living creatures and transparency, as well as first- and second-class rivers.


If you rely on the information on this page to drink river water, it is safer to call the government office or management group with one call.
River water is affected by various environments, and it is difficult to judge because it is viewed differently depending on the purpose of use, so you are responsible for drinking river water.
Use a portable water purifier as much as possible or boil and drink.

Water quality

The water quality class is an index of river cleanliness judged from living organisms. Therefore, the values such as pH value are irrelevant.
Information such as transparency is stated because it is "approximately", but it is not directly related to the water quality class.

Since the link of the index organism is skipped to Google search, please see the photo by image search. There are many insect-type organisms that are uncomfortable, so please be careful if you are not good at it.

Water quality class I [clean water]

A clear river that makes you want to enter a hot day. There are many plants around.
Transparency: It is transparent and you can see the bottom of the river.

Water quality class II [Some clean water]

Often located near rice fields. Walking on the riverbed is not uncomfortable.
Transparency: slightly cloudy

Water quality class III [Messy water]

Drains and houses may be connected. The bottom of the river is muddy and there is much garbage.
Transparency: cloudy

Water quality class IV [Very messy water]

Often found in factories and towns, the riverbank walls are made of concrete or iron. The bottom of the river is muddy and there is much garbage.
Transparency: Gray and muddy


This is a way to separate the organisms introduced here, but it does not mean that organisms of water class I cannot live in rivers below that. There are even those who grow up in a dirty river just because they have the same race, so it's okay.
And creatures of water class IV can live in beautiful rivers. Because it's a dirty river, I don't live in it, but it's just that the adaptable environment, such as the absence of natural enemies, was a dirty river.

By the way, in the river where both walls and the bottom are paved with concrete, if the amount of water increases, the whole river will increase, if it decreases, the whole will decrease, and the flow velocity is the same speed, so it is deep It is not suitable for living creatures because it is impossible to escape.

MLIT Survey Standards

In addition to the above water quality classification, the Ministry of Land, Infrastructure, Transport and Tourism is looking at the following 4 items.

  • living environment (scientific)
  • human health (whether drinking)
  • biological survey
  • new water quality index (whether unpleasant)

I don't know the living environment well (Hey). We are concerned with biochemical oxygen demand and chemical oxygen demand. It is not well understood.
A person's health is whether or not the water can be read and drunk.
What kind of creatures are alive in biological research?
A new water quality index is used to judge whether people feel uncomfortable. According to the survey results, it is a number that you can drink, but it feels like you shouldn't.

However, I can't really trust the environmental standards because they are about.
For example, there are 18 times as many E. coli cells known as O-157 in Dotonbori, Osaka. However, there is no problem because the number of E. coli is not included in the environmental standards. Like this.

What is a first-class river?

Maybe everyone has heard about first- and second-class rivers.
When you say first-class, it sounds like a big, long and beautiful river, but it doesn't matter if it's beautiful or not.
Simply put, a first-class river is a river managed by the national government (MLIT), and a second-class river is a river managed by a prefecture. Other than that, it is said to be an independent water system and is managed by the municipality.
As for how to divide, it is divided according to the influence on life and economy, and it does not matter how big or beautiful it is.

author photo
Writer : Hashi-ryu

The operator of this site. Prefer military and simple camping gear. He is studying bushcraft exclusively.

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