Potential for drinking water savings through rainwater use: a case study in Brazil

Ribeiro, Laura Michelle Leite; Ghisi, Enedir

doi:10.1590/s1678-86212023000200662

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ARTIGOS • Ambient. constr. 23 (2) • Apr-Jun 2023 • https://doi.org/10.1590/s1678-86212023000200662 copy

Potential for drinking water savings through rainwater use: a case study in Brazil

Potencial de economia de água potável utilizando água da chuva: estudo de caso no Brasil

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

This article assesses the potential for drinking water savings through a rainwater harvesting system for non-potable purposes in a flat. The appliances’ water flows were measured; users made daily notes of water consumption, time of use of each appliance, and the number of times this occurred; and daily readings of the water meter were made over fifteen days. Based on these data, the water end-uses and the average daily consumption were calculated. The measurements showed that the percentage of water for activities that do not require drinking water (toilet flushing, cleaning and washing machine) was 36.5% of the total consumption. Through the Netuno computer programme, the ideal capacities of rainwater tanks were determined for variable and average water consumption. It was found that a 10,000-litre tank provides drinking water savings of 34.8%, fully meeting the demand over 95% of the days. The study showed that, even with a considerable variation in consumption, the ideal capacity of the lower tank and the water savings achieved do not vary significantly when using variable or the average water consumption.

Keywords:
Drinking water savings; Rainwater harvesting; Rainwater storage; Non-potable water demand

Room	End-use	Water flow or capacity	Maximum time of use	Minimum time of use	Average time of use
Bathroom 1	Toilet flushing	0.76 l/s	9s	2s	6s
	Tap	0.05 l/s	2min6s	9s	36s
	Shower	2.7 l/min	14min	5min	7min42s
Bathroom 2	Toilet flushing	0.76 l/s	20s	4s	9s
Bathroom 2	Tap	0.06 l/s	5min03s	16s	49s
Bathroom 3	Toilet flushing	0.76 l/s	40s	6s	18s
	Tap	0.05 l/s	4min	36s	1min44s
	Shower	4.8 l/min	26min58s	4min58s	15min32s
Kitchen	Cooking	4.5 l/min	3min03s	27s	1min25s
	Washing dishes	4.5 l/min	20min10s	5min56s	12min48s
	Drinking	4.5 l/min	2min37s	40s	1min20s
Laundry	Tap	0.07 l/s	1min40s	36s	1min07s
	Washing machine	70 l/cycle	2.5 cycles	1 cycle	1.5 cycles
	Bucket	8 l	21 buckets	1.46 litres (measured)	7 buckets

Room	End-use	Flow	Daily consumption (litres)
Room	End-use	Flow	Day 1	Day 2	Day 3	Day 4	Day 5
Bathroom 1	Toilet flushing	0.76 l/s	5.32	3.8	6.08	6.84	3.04
	Tap	0.05 l/s	2.07	2.92	2.92	2.20	1.98
	Shower	2.7 l/min	13.5	14.08	14.08	17.23	0.00
Bathroom 2	Toilet flushing	0.76 l/s	3.04	12.16	15.20	5.32	10.64
Bathroom 2	Tap	0.06 l/s	3.12	2.40	1.04	2.34	1.75
Bathroom 3	Toilet flushing	0.76 l/s	30.40	19.76	14.44	18.24	20.52
	Tap	0.05 l/s	7.56	9.25	9.30	11.98	3.52
	Shower	4.8 l/min	23.84	59.12	76.32	74.08	83.36
Kitchen	Cooking	4.5 l/min	5.47	6.00	13.72	8.50	7.60
	Washing dishes	4.5 l/min	26.70	42.60	29.02	59.40	34.57
	Drinking	4.5 l/min	3.00	6.00	3.00	6.00	10.00
Laundry	Tap	4.6 l/min	0.00	4.60	4.60	0.00	2.50
	Washing machine	70 l/cycle	0.00	0.00	105.00	0.00	0.00
	General cleaning	8.00 l	0.00	0.00	36.00	0.00	0.00
Total estimated			124.02	182.69	330.72	212.13	179.48
Total measured			120.00	190.00	340.00	220.00	180.00
Difference (%)			3.35	-3.85	-2.73	-3.58	-0.29
Room	End-use	Flow	Daily consumption (litres)
Room	End-use	Flow	Day 6	Day 7	Day 8	Day 9	Day 10
Bathroom 1	Toilet flushing	0.76 l/s	5.32	4.56	5.25	3.04	3.80
	Tap	0.05 l/s	6.30	0.54	0.63	0.58	0.00
	Shower	2.7 l/min	14.80	37.80	15.12	16.15	16.87
Bathroom 2	Toilet flushing	0.76 l/s	12.92	7.60	9.12	3.80	3.80
Bathroom 2	Tap	0.06 l/s	18.20	1.49	3.31	1.04	1.17
Bathroom 3	Toilet flushing	0.76 l/s	5.32	10.50	13.68	6.84	6.84
	Tap	0.05 l/s	4.60	7.14	2.20	2.67	6.76
	Shower	4.8 l/min	70.00	64.24	105.60	72.24	30.08
Kitchen	Cooking	4.5 l/min	10.00	8.00	3.50	2.00	3.00
	Washing dishes	4.5 l/min	63.00	59.55	65.00	49.87	58.52
	Drinking	4.5 l/min	11.80	6.00	3.50	3.50	5.75
Laundry	Tap	4.6 l/min	0.00	0.00	0.00	0.00	0.00
	Washing machine	70 l/cycle	0.00	0.00	0.00	70.00	105.00
	General cleaning	8.00 l	1.46	23.50	133.00	0.00	42.00
Total estimated			223.72	230.92	359.91	231.73	283.59
Total measured			230.00	220.00	350.00	230.00	280.00
Difference (%)			-2.73	4.96	2.83	0.75	1.28
Room	End-use	Flow	Daily consumption (litres)
Room	End-use	Flow	Day 11	Day 12	Day 13	Day 14	Day 15
Bathroom 1	Toilet flushing	0.76 l/s	5.32	3.80	3.80	5.32	1.52
	Tap	0.05 l/s	0.45	0.45	1.62	0.00	0.54
	Shower	2.7 l/min	35.32	21.6	0.00	18.22	35.37
Bathroom 2	Toilet flushing	0.76 l/s	3.80	4.56	4.56	6.84	7.60
Bathroom 2	Tap	0.06 l/s	1.56	2.73	0.97	1.49	1.56
Bathroom 3	Toilet flushing	0.76 l/s	11.40	4.56	10.64	14.44	16.72
	Tap	0.05 l/s	3.76	2.20	2.58	1.83	2.35
	Shower	4.8 l/min	119.84	63.76	69.20	77.28	129.44
Kitchen	Cooking	4.5 l/min	13.45	2.50	6.50	3.20	2.50
	Washing dishes	4.5 l/min	88.12	57.75	79.75	90.75	59.25
	Drinking	4.5 l/min	9.00	5.20	6.50	6.15	4.50
Laundry	Tap	4.6 l/min	0.00	7.00	0.00	0.00	0.00
	Washing machine	70 l/cycle	140.00	105.00	0.00	0.00	175.00
	General cleaning	8.00 l	7.00	0.00	0.00	0.00	168.00
Total estimated			439.02	281.11	186.12	225.52	604.35
Total measured			440.00	290.00	170.00	220.00	590.00
Difference (%)			-0.22	-3.07	9.48	2.51	2.43

Month	Potential for drinking water savings (%)	*Average daily rainwater consumption (l/capita.day)*	*Average daily drinking water consumption (l/capita.day)*	*Total rainwater spilled out (l/capita.day)*	Days when the rainwater demand is completely met (%)	Average monthly rainfall in Belo Horizonte (mm)
January	36.50	99.48	173.08	664.43	100.00	309
February	36.50	99.27	172.70	658.11	100.00	186
March	36.50	99.46	173.04	241.18	100.00	219
April	36.50	99.43	172.92	36.73	100.00	93
May	36.50	99.81	173.64	6.30	100.00	29
June	35.98	98.29	174.88	0.00	98.19	12
July	32.86	89.18	182.23	0.00	90.09	7
August	24.67	67.09	204.87	11.55	66.82	10
September	32.51	88.27	183.26	200.16	88.44	42
October	36.50	99.76	173.55	683.81	100.00	151
November	36.50	99.43	172.97	1,220.66	100.00	243
December	36.50	99.28	172.73	915.70	100.00	374
Average	34.82	94.84	177.55	384.56	95.44	140
*Total in a year (per capita)*	-	34,618	64,805	140,366	-	-

Month	Potential for drinking water savings (%)	*Average daily rainwater consumption (l/capita.day)*	*Average daily drinking water consumption (l/capita.day)*	*Total rainwater spilt (l/capita.day)*	Days when the rainwater demand is completely met (%)	Average monthly rainfall in Belo Horizonte (mm)
January	36.50	99.64	173.36	664.10	100.00	309
February	36.50	99.64	173.36	658.21	100.00	186
March	36.50	99.64	173.36	240.80	100.00	219
April	36.50	99.64	173.36	36.92	100.00	93
May	36.50	99.64	173.36	6.66	100.00	29
June	35.88	97.97	175.03	0.00	98.19	12
July	32.98	90.02	182.98	0.00	89.86	7
August	24.53	66.96	206.04	11.66	66.82	10
September	32.52	88.78	184.22	198.79	88.89	42
October	36.50	99.64	173.36	682.88	100.00	151
November	36.50	99.64	173.36	1220.24	100.00	243
December	36.50	99.64	173.36	916.24	100.00	374
Average	34.82	95.02	177.55	384.37	95.46	140
*Total in a year (per capita)*	-	34,682	64,963	140,296	-	-

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[1] Laura Michelle Leite Ribeiro Programa de Pós-Graduação em Engenharia Civil | Universidade Federal de Santa Catarina | Rua João Pio Duarte Silva, s/n, Córrego Grande | Florianópolis - SC - Brasil | CEP 88040-900 | Tel.: (48) 3721-7687 | VoIP: (48) 3721-4842 | E-mail: laura.leite.ribeiro@gmail.com