The Borrowers Afloat

The Borrowers Afloat is a children's fantasy novel by Mary Norton, published in 1959 by Dent in the UK and Harcourt in the US. It was the third of five books in a series that is usually called "The Borrowers", inaugurated by "The Borrowers" in 1952.
Plot.
In this third of the "Borrowers" series, the Clock family begins living in the house of a human boy named Tom. The borrowers find that they will starve because Tom and his uncle are moving away. They need to leave but Tom's pet weasel or ferret is outside the door. Luckily, the animal still has the bell that Tom put on it, but they know they cannot outrun such a swift animal. Just when things are looking grim, Spiller returns via a secret passage: he has come through the drains underneath the house. Spiller says that he has not told the rest of the borrowers about the drains because they never asked.
While deciding where to go, Spiller tells them that they might go to Little Fordham which is actually a replica village. The place has been a bit of a legend with all Borrowers: a whole village made for Borrower size residents with plenty of food from the visiting big people.
Spiller lets them stay in one of his hide out places, a tea kettle, while he goes and investigates the matter for them. During the waiting period, the rain comes down and causes the kettle to be put adrift downstream. The Clocks decide that their best chances are to hope that Spiller will realize what has happened and find them. For the most part there aren't many frightening adventures, but they lose the kettle some time after it gets stuck in some rubbish.
But while still on the river, Mild Eye, the gypsy who nearly caught them before, discovers them. The Clock family is trapped; as none of them can swim.