Q: I am traveling, and there is no keilim mikvah in this area. May I tovel new utensils in a lake or river?
A: Metal, glass and glazed ceramic utensils which are purchased from a non-Jew and are used in the preparation and consumption of food require tevila before use. A person may tovel utensils in “spring water” – water that flows naturally from under the ground. If a river has such water as its source, he can tovel his utensils in the river. The river must contain at least forty se’ah of water, which calculates as 175 gallons of water. An ocean or sea is halachically considered to be “spring water.” Therefore, a person may tovel utensils in an ocean, sea, or river which has such water as its source. However, regarding a river which has “spring water” as its source, if it has recently rained so heavily that there is a possibility that there is more rain water (and rain water runoff) than spring water present in the river, he cannot tovel utensils at that time.
A person may tovel utensils in a naturally occurring lake or in a man-made lake which has naturally filled with rain water. As with spring water, the lake must contain at least 175 gallons of water. However, there is a major difference between tevila in spring water and tevila in a lake. Although tevila in spring water is permissible when water is flowing, tevila in a lake is valid only when the water is stagnant.
It is common for lakes to have drainage pipes in order to prevent water from overflowing when it rains. When water is draining through those pipes, the water above the pipes is not stagnant, whereas the water below the pipes is stagnant. If there are 175 gallons of stagnant water below the pipes, a Sefardi may tovel his utensils in all of the water in the lake, including in the water above the pipes. An Ashkenazi, however, cannot tovel his utensils in any of the water in the lake, including in the water below the pipes.
A person may not tovel utensils in a man-made lake which had been filled with water that was piped in from a nearby water source. It can be hard to find out how a lake was filled and to ascertain that no drainage is taking place. A person should therefore avoid performing tevilas keilim in a lake without first investigating these issues.
To summarize: A person may tovel utensils in an ocean or sea. If it has not rained heavily recently he may also tovel utensils in a river which has an ocean or sea as its source, or in a river which flows naturally from under the ground. He should not tovel utensils in a lake without first investigating how it was formed. An Ashkenazi would need to investigate the drainage issues, as well.
 עי’ בשו”ע יו”ד סי’ קכ פרטי הדינים
 שו”ע שם סעי’ א
 בשו”ע שם מבואר שהמעיין צריך ארבעים סאה מים, ובשיעורין של תורה כתב שאמה הוא 58 צ”מ, ולפי”ז שיעור מקוה שהוא אמה על אמה ברום ג’ אמות הוא 586 ליטר. אמנם החמיר שם וכתב ששיעור מקוה הוא לא פחות מן 750 ליטר ובשעת הדחק עכ”פ לא יפחתו מן 648 ליטר.
 שו”ע שם סעי’ ה
 שו”ע שם סי’ רא סעי’ ב. ועי’ היטב מש”כ בזה הגר”י בעלסקי שליט”א בשו”ת שלחן הלוי פרק כד אות לז.
 ש”ך שם ס”ק יב
 שו”ע שם סעי א
 שו”ע ורמ”א שם סעי’ ב
 שו”ע שם סעי’ נ
 לחם ושמלה שם שמלה ס”ק פו ושו”ת אמרי יושר ח”א סי’ קל
 רמ”א שם סעי’ נ
 לחם ושמלה שם שמלה ס”ק פז ומרחשת ח”א סי’ לט אות טז
 שו”ע שם סעי’ ג