Rain is pelting the observation deck, falling in sheets so thick we can barely see where the Mekong meets the shore.

It is cosy weather and I could be reclined on a leather lounge chair, watching one of the 400 movies in the vessel's eight-seat cinema.

I could also be playing foosball in the game room, reading a book from the library or enjoying a massage in the full-service spa.

Instead, I am sitting on deck, cocooned in a towel against the fierce spray of water blowing in under the canopy, and watching the slate-coloured sky release thunderous amounts of rain into the delta.

The Mekong flows 4,350km through six territories, from Tibet to the South China Sea. To soak in this fluid perspective of the region, I am aboard the Aqua Mekong, a luxury river expedition vessel which has plied the southern waters of the Mekong river since last October.

The four-night, 290km cruise takes me up the river from Ho Chi Minh City in Vietnam to Phnom Penh in Cambodia.

At the moment, we are anchored at the border of Cambodia, and for the next couple of hours we have nowhere to go while immigration officers are on board, sorting through the passports of guests and crew.

There are worse places to be than a floating luxury boutique hotel.

The 62.4m ship has 20 spacious air-conditioned suites, each with a double-sink en-suite bathroom, king-size beds and floor-to-ceiling windows for full views of the river. Eight suites have balconies with a divan and table for two, where guests can sit with a bottle of wine and watch the world float by.

Instead of a balcony, my suite has a 4m-long sofa next to panoramic windows, where I can put up my feet and relax.

Every aspect of the cruise is organised to suit the needs and tastes of the well-travelled connoisseur. The rich decor of dark wood, clean lines and silk, accented by lotus blossoms and Buddha statues, is contemporary Italian meets Cambodian-luxe.

The bar is stocked with top-quality international wines and unique Mekong-inspired cocktails, specially created for the Aqua Mekong by award-winning mixologists from the 28 HongKong Street cocktail bar in Singapore.

Highlights include the Mekong Colada, with fresh passionfruit, mango, lime and coconut; and the Mu Pho Mary, a slightly sweet version of the Bloody Mary infused with star anise and other spices of Vietnam's famous pho noodle soup.

The friendly, attentive service is top-notch and the staff are quick to learn the names of every guest on board.

There are 40 Vietnamese and Cambodian crew members, including a cruise director, paramedic and four English-speaking guides, allowing a one-to-one ratio to the ship's maximum guest capacity.

Eventually, I move through the plush lounge on the upper deck and down a sweeping spiral staircase to the restaurant, where head chef Adrian Broadhead and sous chef Sa Em are leading a cooking demonstration.

A handful of guests have gathered to learn about and taste tropical fruits such as mangosteen and snakeskin fruit, which are new to some, before we try our hand at making Vietnamese spring rolls.

It is a pleasant, restful way to spend the afternoon on what has been a busy itinerary so far.

The day before, our first full day on board, chef Broadhead had led us on a tour of Sa Dec wet market.

A few of us are given small strips of paper with English phrases and their Vietnamese translation so we can help procure ingredients such as lemons, Thai basil and zucchini for the chef.

Our embarrassing attempts at the language are lost on the locals, but it is an amusing way to get a sense of daily life in Sa Dec, a river port and trading centre.

The late French writer Marguerite Duras lived in Sa Dec as a teenager between 1928 and 1932, while her mother taught at a school nearby. It was here that she met Huynh Thuy Le, son of a wealthy Chinese merchant, and began their ill-fated affair which was later the inspiration for her award-winning novel, The Lover (1984).

The Huynh family house (225A Nguyen Hue Road, Ward 2, Sa Dec Town) still stands in Sa Dec - after many years as a government office, it became a small museum dedicated to the couple in 2007 - where a guide tells us their story and also highlights the stratified nature of society at the time and the history of the Huynh family.

Forced to leave Vietnam during the war in the early 1970s, much of the family settled in the United States, where they still live today.

The 120-year-old house shows signs of its owner's former wealth - ornately carved and gilded door frames, floor tiles imported from France - but the gold is dull and some tiles are cracked.

There are chips in some of the picture frames which hang in the front parlour, holding pictures of the Huynh family on one side and pictures of Duras and clips from the novel's 1992 movie-adaptation on the other.

Like the house, with its blend of Western, Chinese and Vietnamese architecture, the family's story of colonial relationships and wartime hardships parallel a distinct era of Vietnamese history.

In the afternoon, we visit My An Hung village and see another rural side of life on the Mekong. Our skiff from the Aqua Mekong drops us on the riverbank, where we walk through a field of chilli padi and rows of banana trees to the village.

The homes are simple and rustic, corrugated roofs and wooden structures colourfully painted in shades of teal and cornflower blue.

We cross one of the many canals which bisect the Mekong's islands and are warmly greeted by a smiling woman in her 60s, whose name I never learn. After serving a table of fresh fruit, she leads us into her home to watch a performance of Don Ca Tai Tu, a type of folk song native to the Mekong Delta.

She sings, high-pitched and plaintively, about love and life in the delta with her husband of 42 years. Our Vietnamese guide Charyia Thach says these songs, which are dear to the southern Vietnamese, are mostly performed by amateur singers as a form of entertainment in villages.

"The songs are about love during wartime, about separation. They reflect the country's history and its ways of life and are very emotional songs. They don't write songs like this today. Instead, young people sing pop songs which sound like they could come from anywhere," he says.

Dressed in a white and indigo floral pyjama set, her greying hair parted neatly and tied in a chignon, the woman beams as she sings and looks lovingly at her husband strumming his guitar. Some missed and off-key notes elicit titters from some guests, but I find the performance incredibly charming.

Later, a few of us take a bicycle ride through some of the neighbouring villages. It is less agricultural than anticipated for an area called Vietnam's rice bowl, but it is a pleasant ride nonetheless. We bike along back lanes, on unpaved and gravel roads past residences and shops, then do as the locals do and pile onto a ferry to cross the river.

We cycle 16km to the other end of the island, where we are picked up, sweaty and exhausted, by the skiff. Cold towels and iced drinks are handed out on board, but all anyone can talk about is taking a refreshing dip in the plunge pool on deck.

A bicycle ride on the banks of the Mekong is a daily option on the itinerary and an ideal way to experience the region's countryside. Though there is a gym on board, cycling is also a welcome way to exercise and burn off our indulgent meals.

Every meal on the Aqua Mekong is an event, a foodie's paradise. The ship's restaurant is helmed by executive chef David Thompson, the culinary superstar behind the award-winning Thai restaurant Nahm in Bangkok.

Though chef Thompson is not always in the Aqua Mekong's kitchen, the recipes are his own, executed in the capable hands of fellow Australian chef Broadhead.

Served family style, every dish, whether Thai, Vietnamese, Cambodian or Western, is fresh and full of flavour. Everything, from the beef pho, to pomelo and squid salad and goat cheese ravioli with shaved parmesan and brown butter sauce, is exquisite.

Chef Broadhead modestly says credit is due to Thompson's ability to perfectly balance the flavours of any dish. I am stuffed to the gills by the end of the trip and earnestly wish his food is less delicious.

Back at the border, as if ordained by the river gods, the rain relents as we start to move again.

Tawny water laps at the shore and in the heat of the afternoon, steam is rising from the unbroken expanse of jungle on either side of the river. It is quiet, mystical and calm, a complete contrast to Vietnam, where the Mekong is industrious.

The smoke stacks on the banks signal the country's progress, fish farms line canals like aquatic villages and the waterways are busy with boats ferrying goods to factories, the rumble of their engines an indispensable part of the river's chorus.

But here, on the Cambodian side, the treetops define the landscape and the few boats we see are smaller, more discreet. As the sun sets peacefully on the horizon, it is as though, in the rain, the river has been reborn.

The next day, we take a tuk-tuk ride to a local temple, where smiling primary school children are learning the Cambodian alphabet.

They are polite and follow instructions until recess is called and they scamper out of the windows, eager to climb trees and chase one another around the temple's courtyard. They are clamorous, inquisitive and uplifting to be around.

Back in the tuk-tuks, we drive past rice fields and through small but prosperous Cambodian villages to a nearby silk centre.

The scene is once again quiet and bucolic, and when we enter the tree-lined silk centre for a tour of the silk-making process, the only sound is the occasional thud of sun-ripened mangoes falling from the trees. One drops directly in our path and we pass it around, peeling back its skin to bite into the warm, sweet flesh.

It is a hot day, oppressively so, and the dry cackle of crickets rises like the temperature as we are shown young silkworms eating mulberry leaves. Women are harvesting spools of silk and weaving vibrant shades of blue, purple and pink at the loom. Around the corner, hammocks hang, tantalising in the shade.

It is this quiet countryside view of Cambodia, away from the overwhelming throng of tourists and traffic, which I appreciate most.

The Aqua Mekong guides actively seek out these off-beat experiences and we are always warmly received, never harassed. Most of the time, we are the only tourists around, which makes our Mekong experience feel decidedly authentic.

Our trip ends in Phnom Penh, but I wish I can continue on to Siem Reap, a tour available only during the high-water season between July and November.

Though there are a few teething issues to work out on board - maintenance, mainly, as the boat adjusts to its tropical home - few cruises compare with the considerate, detailed approach of the Aqua Mekong. Waterways are the life blood of civilisations, and the Aqua Mekong carries me into the heart of the region.

•The writer's trip was sponsored by Aqua Expeditions.

This is the second of a four-part Voyages series on the best boat trips in the region.

For sights and sounds along the Mekong River, go to str.sg/Z5fZ