A slow Sunday lunch tastes better within sight of water. There is something about a riverbank garden — the light moving on the surface, the occasional clatter of a moorhen, the sense that nothing needs to happen quickly — that makes even a decent roast feel like an occasion. The trick is choosing well, booking early and leaving room for a stroll afterwards. What follows is practical advice drawn from years of pottering along British waterways in search of the perfect post-lunch amble.

Pick your stretch of water first

The pub matters, but the river comes first. A gentle, navigable waterway such as the Great Ouse, the Avon or the upper Thames gives you flat towpaths, lock-side benches and easy walking after eating. A chalk stream in Hampshire or Wiltshire offers clearer water, watercress beds and a sense of privacy, though the banks are often narrow and the fishing rights strictly private. Tidal stretches — parts of the Thames, the Deben, the estuaries of the West Country — bring mudflats, wading birds and a rhythm set by the tide tables rather than the clock.

Ask yourself two questions before you shortlist anywhere. Can you walk twenty minutes without needing a road? And is there a bench, a bridge or a churchyard within that walk where you can sit down again? If the answer to both is yes, you have found a proper Sunday pub.

What to look for in the kitchen

Waterside pubs are not automatically good pubs. Some trade entirely on the view, and you can usually spot them by a menu that runs from lasagne to katsu curry. A better signal is a short menu that changes with the season and mentions where things come from — a named farm for the beef, a smokehouse for the haddock, a local grower for the purple sprouting broccoli in February.

• Sunday roasts: ask whether the meat is roasted on the bone and whether the Yorkshire puddings are made to order. If the roast runs out at half past two, that is a good sign, not a bad one.
• Fish: on the coast, look for day-boat landings and a note about the harbour; inland, expect trout, pike-perch or smoked fish rather than sea bass flown in from nowhere.
• Vegetables: a decent waterside kitchen will have at least three vegetable sides that are worth ordering on their own — buttered greens, roast roots with honey, new potatoes with mint.
• Puddings: sticky toffee, crumble, rice pudding, a proper cheese board. Anything made in-house and served warm is usually the safest bet.

Non-drinkers are better served than they used to be. Ask for a local pressed apple juice, a decent alcohol-free beer or a pot of loose-leaf tea, and you will often find the kitchen has thought about it.

Booking ahead without the fuss

Sunday lunch is the busiest sitting of the week, and waterside tables are the first to go. Between May and September, and on any bank holiday weekend, ring or book online two to three weeks ahead for a table between noon and one o'clock. For Mothering Sunday, Easter, Father's Day and the Sunday before Christmas, think six to eight weeks.

• Ask specifically for a garden or terrace table — many booking systems default to indoors, and the riverside spots are allocated by hand.
• Request the second sitting, usually around two o'clock, if you want a quieter room and a more relaxed kitchen.
• Confirm whether a deposit or card hold applies, and what the cancellation window is. Twenty-four to forty-eight hours is now standard.
• Mention dogs, pushchairs, high chairs and mobility needs when you book, not on arrival. Riverside steps and gravel paths catch people out.
• Check the tide table on tidal rivers and the river level after heavy rain. A garden that floods at spring tide is not the garden you want in November.

Turn up ten minutes early. Car parks at popular waterside pubs fill fast, and the overflow is often a muddy field a quarter of a mile away.

The walk afterwards

Build the stroll into the plan rather than deciding over coffee. A good post-lunch walk is forty-five minutes to an hour and a half, mostly flat, with a clear turning point. Towpaths, dismantled railway lines, riverside meadows and estate tracks all work well. Take wellington boots from October to April, a torch in the shoulder seasons, and a paper map if the footpath signs are likely to be worn.

Look out for the small histories you would otherwise miss: the brick footing of a vanished mill, a lock-keeper's cottage with its windows bricked up, a ferry crossing marked only by two posts on opposite banks. Many of these appear on old Ordnance Survey maps but nowhere else, which is half the pleasure.

A small ritual worth keeping

Choose one river, one inn and one walk, and return to it through the year. You will learn when the swallows arrive, when the banks are thick with meadowsweet, and which table catches the last of the evening sun in September. Book early for the busy months, keep the walk short enough to be tempting, and let the afternoon take its time. That, more than any menu, is what a slow Sunday by the water is for.