Some of the techniques you can use to reduce the amount you have to water are long term rather than quick fixes.

You need to ensure your soil has plenty of organic matter in as this is what can help hold water.

Some plants are specifically planted over a trench of rich organic matter: runner beans do well if you dig and fill a trench with either kitchen waste of manure. This needs to be done a few months before you plant out the beans. The organic material acts as a reservoir of water for the plants to put their roots into. This helps the beans keep the moist roots they like to have to allow them to set beans.
The amount of organic material in the soil also soaks up water when you are able to water. Watering when the beans are setting is helpful for improving yield.

By double digging you are able to include plenty of organic material in to the soil. You can use garden compost or well rotted manure.
The no dig method uses mulching on the surface and allows the worms to take in the material to the soil. As the mulch rots it increases the soil depth and will provide a layer to prevent water evaporation. Mulching around plants can help conserve water.

Planting so the plant sits in a slight dip makes watering more effective. The water is guided to the stem and roots. Some plants do not like the stems getting wet so these need to be on a mound. Use a plastic bottle submerged upside down as a way of getting water to the roots.
I plant my courgettes and pumpkins on mounds that are full of layers of organic material. This means they will be able to absorb plenty of water from the rich soil.

If you don’t water plants and the soil is lacking in organic material then plants will tend towards going to seed more quickly. Bolting happens when plants are stressed. If you have no water on your allotment site then it becomes clear why you should enrich the soil as much as possible so that the plants have access to more moisture.