Drinkingwater had to be brought from the nearby rivers. The underlined word is a -

Verb এর সাথে ing যোগ হয়ে যদি noun এর কাজ করে অর্থাৎ Verb ও noun এর কাজ করে, তাহলে তাকে Gerund বলে।
সংক্ষেপে: Gerund = Verb + ing = noun = Verb + noun.
এই বাক্যে 'Drinking' শব্দটি Gerund হবে।

** Sometimes it is difficult to distinguish between a present participle and a gerund, since gerunds can also be used as adjectives.
For example:
In the phrase 'Drinking water' the word 'Drinking' is a gerund used as an adjective.
- We know this because, drinking water means water that is used for drinking.
- It is not a present participle because the water is not doing the action of drinking.

Lets see another example:
- He dived into the swimming pool.
- He waved to the swimming children.

In the first sentence, the pool is used for swimming. So it is a Gerund.
In the second sentence, children are doing the action of swimming. So it is a Present Participle.

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Here are some other examples of gerunds used as adjectives:
- Sewing machine
- Frying pan
- Baking sheet
- Fishing rod
- Bathing suit
- Shaving cream
- Ironing board
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• The + verb+ing + of = verbal noun.
- Verbal Noun দ্বারা Noun এর কাজ সম্পন্ন হয়।


Source: Gmat Club and Applied English Grammar and Composition, P.C Das